What are your favoruite Ults? I've only used 7 or so heroes, but I really like Slardar's, Sniper's and Phantom Assassin's
I overlooked Slardar's for a while as I've never really played any game outting much focus on weakening the enemies, always preferring to buff my own guys. But ganking is much more effective when you pull out that Armour Reduction
Sniper's goes without saying. Huge range, difficult to dodge, massive damage. Great for initiating if you have teammates following up, great for finishing them off, and great for basically forcing an individual enemy to retreat
Phantom Assassin is the only one I've played with a Passive Ult, and it makes it so quick to push a tower once you get your attack speed up. Plus, it just looks so cool
Could never really get into a position to use Sand King's properly without taking too much damage while channeling, and struggled to use ven's effectively as well, with the enemy often just running away as soon as I used it. Probably much better when you have coordination with your team for them to slow the enemy down while you move in with your bonus damage.