I like the potential sustain-heaviness of both classes.
Ferals have a pretty good host of bleeds and a good Covenant ability in Adaptive Swarm, plus they’re incredibly mobile with tons of Utility.
Or
Assassination Rogues have Wound Poison and Dashing Scoundrel as a Legendary, which makes the poison applications hit harder with some energy generation as well. While not as mobile OR as useful in non-combat things, Vanish and Cloak can’t be ignored.
NE Druid so you get a wanna-be vanish along with the Druid perks! As much as I hate to say it my Druid is the character I have that feels the most rounded and able to do whatever.
Roll both, see which you like best.
Druids get convoke.
Need i say more?
I’m leveling both right now and each have their pro’s and con’s.
Sin feels great when you’re on a target, but Feral can run away from most problems and they have the far, far superior heal.
Part of me wants to go Feral, but harassing healers with Wound Poison is just so much fun.
I bet every rogue rejoiced when they removed poison cleansing totem… 
Played both for a bit, and assassin feels like it gets a full, cohesive kit complete with quality of life things for a dot spec… And necrolord feral does not. I kept noticing things I wish feral had.
Sin dots give energy back. A lot of energy. In fact, energy generation is so much better with sin, it’s silly. Sin gets slice n dice (Savage roar is roughly equivalent) without having to talent for it. Their version of primal wrath is on a talent line where you don’t have to give up something extremely strong to choose it, unlike feral.
I enjoy them both and would prefer feral druid, but sin rogue feels far better unless you really, really want the druid things like heals.
What decided me is the public perception, which is unfortunately a thing in any pugging. I didn’t want to try to drag down my guild by bringing another low geared alt, so I went the pug route to get initial gear. I kept running into problems with feral getting invited to even yolo RBGs or M+. Rogue was invited instantly with even less gear.
Sin seems legitimately good in PvP and raid now. You can do okay in m+ with sin, or go outlaw and be what seems to be the new aoe hotness.
Feral has to work very hard to be close to that, and it feels super awkward for various reasons, not the least of which is energy regen so terrible feral players have to owlweave to have a chance at optimal dps.
Oh, and feral need far too many legendaries to cover all situations, it’s silly. Sin needs one, maybe two to cover all raid and PvP situations. So sin rogue would be easier to get into, as well.
But hey, try them both and play what you want. Some gifted ferals are topping meters on certain raid fights, though they are crazy good players who eek every drop out of the spec, so ymmv.