From what I've experienced Reddit only has a positive reputation amongst people who a) only browse a handful of reddits and thus have zero clue about the mewling shit-heap that lurks below the surface, or b) people who actively use reddit non-stop and are thus neckbeard-deep in the shit-stew they've cooked up for themselves. Everyone else seems to know it's a horrible place, and just browses the subreddits that aren't colossal shitstorms/appropriately moderated.
Tumblr is fascinating since all the channers and redditors keep playing up how they're the ones who hated it first, but honestly having used Tumblr for... fuck, 6 years now, I think, the bad rep of Tumblr comes from Tumblr itself. Everyone on Tumblr knows it's a shit-hole of internet discourse, personal attacks and porn-bots, but since you can tailor it so you only see content you want to see, nobody really cares about all the 14 year olds calling each other 'pedophile' and just follow all the blogs that post cats/pretty art/tits/video games/gardening/frogs/fashion/whatever.
Nobody hates Tumblr more than people who use Tumblr. Nobody. Well, ok, maybe the staff.