So I personally like Diamonds Yet they aren’t “making them anymore” .
Signature Cards are really nice I recently got The Starcraft & the Neutral Ship Signatures at the Start of Great Beyond. *got a 15 bucks off mobile version cause I was gonna hold off on the purchase & another offer appeared payed 12$ for it Super way worth it anyway…
I felt The Starcraft & Neutral Ship Signatures held “value” since it gave you all the signature Ships & the starcraft cards are played thru all the classes.
I like that you can see the Full Art of the Card yet the Border is so ugly 
compared to the Diamond Cards even Gold cards Shine better Than the Signature border its very lack luster.
My suggestion would be that the Border Glow like one of those Florescent colors like those deep purple or greens Wow is good at doing. Or even let us choose the color.
Wish they would change the boring sand in the background as well
I always assumed they make diamond and signature card art each card release expansion are you sure they are no longer making diamond cards
Regarding diamond portraits those are cool to me the standout diamond hero portraits are the new Gen portrait the diamond Malygos mage portrait and i actualy liked the first hunter diamond portrait very cool 
those are my top 3 but not the only ones i like
To anwser your question i like both signature and diamond cards.
I think they are making Diamond Heros portraits yet no more Diamond Cards they were shifted out for Signature Cards they explained it in one of the patches a while back I think Old god signatures.
I am on the fence about getting the worgen warrior/shaman Diamond Portait 25$ aint to bad of a price for how it interacts/changes.
I have the C’thun Portrait for Druid & it was 25$ as well I think & it was way worth it in my eyes wish it had more flare tho like some Diamonds That Start with like a Wildlife Background at the start of game or like kerrigans ending of the slime/creep on the board. Wish it was a permeant board.
I see so they did stop yeh and sorry for the late reply i think both looked good but for me from an artwise perspective signature art have more potential since there are many ways to do art.
The Genn skin is pretty cool like i said earlier
If you look at the new Tyrande signature u can see its abit different then say the Deathknigt Legendary Nythendra but both look cool.
Thats the main plus point of signature cards u have many artstyles to express artistic flair
I hope there is a way to view signature cards on playhearthstone site i dont think there hopefully its added if possible or they just show both.
I think both are ugly and never understood why people would want them
I just want to be able to DE them both.