I like adv/disadv. It's incredibly simple and balanced for "I don't want to overthink it" situations. If a player has a good idea or does something dumb, I throw adv/disadv at them and call it a day. If it's something they do repeatedly, I come up with a standard modifier for it. The group is aware of this attitude and okay with the target being adjustable. My biggest concern is that the Rogue is the most tactically creative player, so I have to think about whether Sneak Attack is also warranted; if not, he just gets a +/-2.
I didn't like it at first, but I've come to believe that the non-stackable/single-cancel nature of adv/disadv is a feature not a bug. It keeps things from getting out of hand when players are really, really creative (or rules-lawyery). A situational +/-2 is probably just as balanced as adv/disadv, but could be argued into a stack. Unless the GM is a real jerk, that's going to work in the players' favor, over the long run, and probably be unbalanced.
Another reason I like adv/disadv, is that it actually gives a bell curve benefit, with an effective bonus of +5, when you need to roll a 10 to succeed, but an effective +1 at the ends. It feels like a nice bonus all the time, though. Why is this a good thing? Because I don't like coin-flips. If the players already have a good chance of succeeding, then I'm entertained by a good idea, but there's no point in giving a huge reward. If it's a good enough idea, I'll probably just give them an auto-success; if not, they still have a chance of dramatic failure. If it's a bad situation, then they should probably come up with something more significant than clever positioning on a single roll to get out of it, but every little bit is worth something. If it's a middle-of-the-road challenge that boils down to a single roll, then a good idea is perfect for moving a 50% chance of success to a 75% chance. No matter what, though, a clever idea always gets a boost -- and I can use the same mechanic to do it.
As might be apparent, I tend to give out more advantage than disadvantage. It's just more fun. Ad hoc disadvantage generally comes in the form of players spending their Inspiration die to penalize an NPC. I don't think this is an official use for Inspiration, but it's been really good, especially the way we handle Inspiration. I went out and bought a handful of the ugliest dice I could find and assigned one to each player. When they gain Inspiration, I toss them their die. When they use Inspiration, they roll the die and then toss it to me. Inspiration is always rolled by the player, even if the other die is rolled behind the screen. That means the players can use inspiration to gain strategic information about major NPCs. It also ensures that there's no way for me to "dramatically fudge" the roll (whether or not I would is beside the point). It may sound like a small, niche thing, but my players got really excited when they realize the implications of the ruling. That's what matters.