Who are you playing? I play ADC all the time and have a ton of fun, and I generally do decently well, too. I also extremely rarely duo. I play a lot of Twitch and Miss Fortune as my ranked ADCs and Vayne, Varus, or Lucian when i'm looking for some fun in normals. Overall, it's a very hard role to learn, but it's pretty rewarding once you learn it, because you know as a fact that you can carry any game if it runs long enough and you position properly. However, it's also among the highest skill cap roles. If you want some freelo, play Miss Fortune. You're strong in lane phase, so you aren't reliant on your support to do the right thing anywhere near to as much, you just rely on them not feeding, and you're a teamfight god who can take over a game with just 2 items. Plus, even with the change to Youmuu's and Duskblade, the armor pen build on her will still be good. Youmuu's -> Duskblade -> Black Cleaver -> Last Whisper. Your ult will easily be going above 4000 damage and you'll be doing basically true damage to anyone no matter how much armor they build (each wave of ult applies a stack of Black Cleaver's armor shred = 30% reduced armor + LW's 40% + Youmuu's and Duskblade). Throw on a Death's Dance or Edge of Night and you'll become basically unkillable while you channel your ult, too. For masteries, 18/12/0, picking up DFG (it applies the AoE on your ult, the DoT on your E, and the single target on your Q; the AoE on ult also refreshes itself every tick of the ult, adding a ton more damage onto it). You do too much damage while also being tough to kill.
On the flip side, if you want to truly LEARN the role well (MF is one of the least mechanically intensive champs in the game, you just have to know when to ult and then do it), play Vayne. For her, a single build is far less easy to pick because she can build a lot of things, but right now I recommend a crit burst build. You get BF Sword into either Statikk Shiv or RFC, then IE, and then PD. Tons of attack speed, tons of burst on that first auto, tons of damage on the third. You can also go a very lifesteal-heavy build to avoid punishment, rushing Runaan's (lifesteal applies fully on the 3 bolts from it) into just as much lifesteal as you can pile onto her and now you have so much you're difficult to kill if you keep autoing, especially if you use your ult and Q properly in fights. For masteries, you can go 18/12/0 getting either Fervor or Warlord's, depending on if the enemy team is tank-heavy or not, but right now I would recommend Warlord's. Vayne is a very mechanical, skill-intensive champion. You can do some pretty amazing stuff on her if you learn her right, but the road to getting there will be long and hard. I have mastery 4 on her, pretty close to mastery 5, and I still don't have Vayne mechanics down perfectly. However, if you can play Vayne well, you can play any ADC in the game well.
Another thing you can do is a roam gank Twitch. I don't do this when I play him, but I should, since Twitch is one of the few ADC's who can roam and snowball himself with other lanes as well, and he's strong with a snowball. Basically, you get your Serrated Dirk -> Runaan's -> Youmuu's and just constantly shove the bot lane in, then go mid with your stealth and get kills there. You play kinda like a jungler in that sense, where you don't really snowball off your own lane, but you do it by putting the enemy mid laner behind and getting your's ahead. This is a way to have a strong early impact, and I might even do this as early as level 3 if I can without getting punished too hard. It's a pretty decent way to do things, and it's a lot better than the farm and carry later style that Twitch normally has. Honestly, I feel like this is the biggest reason why Twitch started building Youmuu's, but so few people do it anymore that they may as well just do crit build instead if they don't. I know Twitch is definitely going to switch to crit build after the preseason changes instead of Youmuu's rush because Youmuu's is losing the attack speed. I'm not sure how that would affect her DPS, but it's something I'm interested to see tried. Twitch could do something similar, except throw a Runaan's in there early, too. His stealth resets would make the Duskblade pretty decent. However, he's also pretty attack speed reliant, so it might lower his overall DPS in teamfights and force him to play more like a Vayne if he does it. I wouldn't be surprised to see Twitches rushing Runaan's -> IE -> Statikk/PD in the preseason and the next season. A lot of attack speed, but it's a much later spike than what he has now, however with Youmuu's active not giving attack speed anymore, it might be necessary.
Overall, ADC is in a bit of a tough spot right now. You can carry if the game runs long enough and you're good, but for most ADC's, that's not an easy task. I'm interested to see a number of new builds pop up after the preseason changes. Maybe I'm wrong about Twitch just going crit instead of Youmuu's rush, and he'll do a full armor pen build and play like an assassin still. Maybe Vayne will do the same thing, Youmuu's -> Duskblade -> Edge of Night. Yes, for the new Duskblade passive, she does have to be in stealth for 1 second, but there's literally 0 attack speed in that build, so she may as well stay in the stealth; she won't lose too much DPS, and it's quite a lot of bonus true damage.
