There’s a number of different ideas I tend to follow when fighting BH against Sentinel when both have Commando.
By and large, Dasrik’s remarks that you should only call Commando when they do are accurate. Unless I see a Sentinel just having a humongous droolfest for wanting to stay right over my head I don’t usually call Commando first much. Punishing their Commando bit by bit is always a plus.
And yes, Sentinel is going to control the horizontal most of the time, so you want to stay on the move and play the air and ground, wherever he isn’t. BH’s tail pokes, indeed, are basically going to win over everything Sentinel has at close range, so if you can keep on the move and keep close to him, and when you can’t keep close to him, keep the demons floating around so that he can’t keep at his favorite ranges to you if he’s not going to let you to yours over him, that can make BH vs. Sentinel a lot more even of a fight than a lot of people think.
From there, what you want to eventually work towards depends on what team they’ve got. Any Sentinel is usually going to be in the most trouble if BH can zone him into the corner, but in practice that doesn’t help much. In addition, the usual DHCs of death don’t usually work too well on Sentinel with BH/Sent/Commando (my favored combination). There’s sort of a substitute one where you can throw dark thunder/HOD and then DHC to HSF from that, and it often even works. However, Sentinel has to basically be grounded when first hit for the angle to work right, which means that the air-to-air demon setups for things don’t work worth a damn on Sentinel DHC-wise. On top of that, the HOD is random enough that sometimes they’ll get to roll out of the thing and the HSF whiffs. All of which is intensely irritating.
However, I’ve started toying around with a very different tactic, which just about makes me think that maybe Watts isn’t so bad against Team Scrub after all. If they start Cable on BH, neat… I usually like that better than grinding it out with Sentinel and then forcing my Sentinel to win the game on their Cable most of the time. (Starting Sentinel is not usually a good option in either case.) But if they start Sentinel on BH, that can often get annoying… but then it kind of dawns on me that BH doesn’t have a terribly unrealistic shot at doing what Magneto does to turn this matchup upside down. Specifically, snap the other lugnut the hell out. Works quite efficiently off of the same air-to-air demon hits that lead to deadly DHCs on everyone else, and it’s not out of the realm of difficulty on random hits, either.
No, BH often won’t be able to kill Commando that well, but in a BH/Commando vs. Sentinel/Commando fight where you’ve been doing your job at all well, their Commando is usually going to be hurting when they come in. So the end effect is usually that you whack down half or more of their Commando’s life in redbar and screw up their team order something awful for the rest of the game, which will usually come back to hurt them badly later on even if you don’t kill Commando now.
With something like Sent/Storm/Commando, it’s a little less feasible because Commando has a free out with a DHC to hail. However, if you’ve been doing your job against Sentinel that’s still a bunch of lifebar that you should be knocking out by snapping him in there, which is still worth it all on its own.