It's at this point that I'd like to add that I now own all three in a league I just joined - as an expansion GM - last year. Hi-yo!
But in seriousness:
We don't have a huge book on what Yakupov will do, given he's only had a 48-game season under his belt. I really liked what I saw, but am a bit concerned about all the talent he's playing behind. He may be the best of the bunch (many saying he has more talent than Eberle), but that remains to be seen. I don't really think he's a KHL threat, but that remains to be seen as well. I think he's a legit talent, but there are question marks.
I love what McKinnon has to offer with great speed and skill. And I also think he and Duchene will combine to be a ridiculous one-two punch eventually. To me, he's going to be an absolute star. And he has a few less bodies to climb over than Yakupov does. Any guy who goes #1 in the deepest draft in years is absolutely legit.
Drouin appears to be the heir apparent to StLouis. Clearly, he may not get the chance to play full-time alongside Stamkos until MSL is done, but if/when that happens....well, I can't think of a better place to land. It remains to be seen, though, if his skill level will translate to the bigger/faster NHL game. I think it will, but it may not. But, much like MacKinnon, to be a top-3 pick in this deep draft says something about the kid's value.
I'm really tempted to take the "they'll all be top studs, within 10-15 points of it each in a given year" mindset...but that's kinda a cop-out
So my personal ranking, combining ST and LT:
MacKinnon - I think he surpasses Duchene (who I absolutely love) and puts up big numbers in Col
Yakupov - cannot deny the talent around him in Edmonton, but I think that also slightly affects his numbers
Drouin - simply because I think he'll need to, at the NHL level, be slotted with Stamkos to put up really eye-popping numbers. That will likely happen, but it may take a bit of time. So the short-term numbers might take a hit, affecting Drouin's overall appeal
But, again, I don't think you go wrong with any of the three.