Should I prioritize ilvl or stats
Stats.
At level 70, there will not be a difference. The item with the higher stats WILL always have a higher ilevel. In fact, there is a formula, and the ilevel is calculated from the stats.
This was always true, but as Blizzard went through various squishes and stretches and scalings after each recent expansion, the formula didn’t map evenly between expansions and levels, so that there are all kinds of inconsistencies and corner-cases in gear that drops when levelling before Dragonflight. One piece may have a higher ilevel but lower stats than another from a different expansion in Chromie Time. As far as I know, Blizzard do some invisible cheating when calculating effective stats for levelling characters to somewhat smooth that out. (But level scaling is a complete mess anyway. But levelling doesn’t last long anyway, so most people don’t seem to care much. Ugh.)
But while all stats are created equal, different specs value different stats differently. Does your spec get more out of Haste, or Crit?
For an introduction to valuing each stat for your spec, look at
https://www.icy-veins.com/wow/class-guides
look up your spec, and choose the Stat Priority page for it.
As you get further into content at level 70, and may want to optimize more, you will want to simulate your character to get more personalised stat recommendations that take into account the gear you already have, and the talent build you have chosen. This page explains more:
https://www.icy-veins.com/wow/how-to-sim-your-wow-character-a-guide-to-raidbots
Majority of the time, ilvl will be more important due to primary stat being higher, which is normally the number one stat for all class and spec. But understanding your stat priority for your spec will help you a lot throughout your rotation. items like rings and neck don’t have primary stats, so ilvl isn’t as important. But melee weapons for example, ilvl is more important, even without the correct secondary stat priority. It really depends on a few factors.
If you’re not 100% sure, ilvl will most likely be the way to go if you want to play it safe.
Oh dear. Now we’re going to confuse the newcomer. 
The problem is right there in the words
Majority of the time, ilevel and stats will clearly point in the same direction. The question is about what happens when they don’t.
So if, as an Assa Rogue, you have a 389 Dagger, and you see a 415 Dagger in the AH. The 415 is better, right? Not if the primary stat on it is Intellect instead of Agility.
And, as I said, there are weirdnesses in gear below level 61, and undocumented invisible kludges in the scaling, so it can be impossible for anybody but Blizzard to know what’s actually happening there.
Here is the simple two-condition rule I would use:
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If both items have your spec’s primary stat (Agility for Rogues, and Hunters, and Guardian and Feral Druids, and others; Intellect for Mages and Priests and Holy Paladins and others …) then the one with the MOST of your primary stat is very probably better.
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If neither has your spec’s primary stat (commonly on higher level rings, necks, trinkets) then go with the higher item level, which will almost certainly be the same as higher stats at level 70 except for trinket Procs and On-Use effects. This is more likely than not to be right.
When you get advanced enough at level 70 to really care about a percent or two of performance, use a computer program to simulate your character’s performance with each alternative. Raidbots is an online website that will do this for you.
Huh!? you proceeded to explain how they should sim their stats and that isn’t complicated in itself!?
Not everyone wants to play that way. I approached it in a more casual sense of the game to lessen the confusion, unlike the approach to sending newcomers to download sim addons that is meant for professionals to minimax gameplay.
I go to explain what “Majority of the time” means, indicating Rings and Weapons has a different outlook on ilvl. So yes, majority of the time, ilvl will be prioritized outside of Rings, Neck and Trinkets (anything that doesn’t have your Primary Stat) as stated on my last post. There is nothing confusing about the item will determine if stats or ilvl is more important without sending them to third party sites to sim their dps. which is 100% more confusing. I know players that have been playing for over 10 years that don’t even understand or have not attempted to use Raidbots and they’re doing just fine! That shouldn’t be an option for “Newcomers”, it’ll scare them away from the game more than anything.
To your second point. The audacity to assume our friend, Gerd here does not understand his “Primary stat” to be Agility is quite an insult. His ilvl being 470+ tells me he is well aware a dagger with a higher ilvl in the AH that has intellect will not do as much damage as a weapon with Agility. Mainly because, Agility weapons will naturally have a higher Damage per second if we were to compare Agility and Intellect weapons. The ilvl of a weapon will determine the DPS of the weapon, therefore, ilvl is better for melee weapons.
Their question isn’t, if i get two of the same ilvl gear, which is better?
The question is… Should I prioritize ilvl or stats.
In simple, non confusing terms, ilvl will majority be the safer way to approach the game until you start receiving items of the same ilvl, then stats will be determine on your stat priority in which gear you should equip if they share the same ilvl. But Primary stat is naturally your best stat… which will always be on gear with higher ilvl.
You just reworded my first post.
Why does this have to be stated? Why would they receive anything else besides agility?
I’ve never received any other primary stat that’s outside my spec throughout all content. Even if he played a Paladin, most gear have Primary stat swap when the spec is changed from Ret/Prot to Holy. I completely understand explaining this to someone that just started playing, with a low achievement score, that isn’t level cap. Kind of like the account you’re using right now! But again, that isn’t his question assuming that he knows agility is what he needs. A simple look through his character profile could tell you that they are aware. You could simplify and make it less confusing to them by not bringing the fact that he needs Agility and not Intellect. Funny how you never brought up that point on your first post, instead because my post was so confusing to understand, to make your AH dagger theory to be valid and my post to be irrelevant. You need to make sure he knows he needs to equip agility? great.
This is completely wrong. If neither of your spec’s primary stat is on the item, rings, neck and trinket… DO NOT look at the ilvl.
chances that a BiS trinket with a lower ilvl will most likely be better than a trinket that does not benefit your spec at all.
Same with Rings and Neck, if the two items have different ilvl, assuming the gap between the ilvl are not massive, for example, a Mythic 4/4 (489 ilvl) and a Heroic 6/6 (483 ilvl), the item level difference is not big enough to justify the stat priority.
Assassination rogue stat priority is Agility > Mastery > Crit > Haste > Vers.
If you have a ring with Mastery and Crit at a 483 ilvl, it’s still better than a ring that has Haste and Vers at a 489 ilvl.
so why are you trying to prove me wrong? your post isn’t the only post that has to be “the best” answer. You don’t have to bring me and my post down to justify that you have a better post. if you wish to elaborate on my post because you may be able to see how one could be confused reading it, sure, I wouldn’t have any issues with that. To insult my post by saying how confusing it is and how there are problems with my post and proceed to give false information… that’s just disrespectful.