I was going to say the same thing. I sent my 'cocktail-snob' sister to Chandelier Bar for a quick drink. She likes to play "stump the bartender". They planned on being there 30-45 minutes, stayed 5 hours, blew off the rest of their plans for the night and drank on all the levels.
In April, got the best I have had in LV at the 777. It was about 1700 and the bartender Traci was awesome.
I've had the best one at the Cosmo with muddled cherries a couple of years ago and the last one I had there was last year and I guess I didn't ask about the muddling before hand and it wasn't that great.
Pretty sure I had an old-fashioned at parasol Down and it was really good, but it's been a while (I think that was a 2013 trip). We had been sent to that bar by VMBers because my husband likes to have a good Manhattan when we travel....He did say his drink was worth it. They were NOT cheap ;-) [Old Fashioneds are the bourbon/rye cocktails I get when I'm out - if I'm home, my favorite bourbon/rye cocktail to make is a Ward 8. It's super easy but not common so I don't ask for it when I'm out....2 oz rye, 3/4 oz lemon juice, 3/4 oz orange juice, 1tsp grenadine....]
The best old fashioned I’ve ever had (might’ve been 3) without question was at The Golden Steer a couple of weeks ago.
if you'll be downtown, the Griffin makes a good one. Or at least the bartender that was there on my last trip did. I may have had 3 of them.
Late to this thread, but... Chandelier as others have mentioned. But for something a little different and quite tasty: Zuma resturant in Cosmo makes an amazing one with Japanese whiskey, perhaps my very favorite anywhere Carbone restaurant in Aria makes one with a speciality rum that is also fantastic. Carbone is an outstanding restaurant as well