On Screen buttons = Not bad, but a waste. In some apps looks really bad. Full bar like nexus 4 looks better than just ... though.
Capacitive buttons like HTC = ok, saves screen space, I still miss tactile feel.
Capacitive buttons like Samsung = So dumb... when not lit up you can't tell which is which... and there are 4 of them... and they keep changing the order and functions of those 4. Drives me nutz! (I might not have got the HTC if the back button was on the right like all of Samsung's 3-button new layout... just doesn't make sense in my head... I will never get used to it... back button goes on the left! You can put it on the top-left like iOS or on the bottom-left like all other Androids... why does Samsung put it on the right now!?!?!? Maybe it's just me because I am left handed?) I do kinda like the one physical button in the middle with cap buttons on each side though.
I love the 4 physical rocker-buttons on my SideKick 4G (Home/MT across the top, Back/Menu across the bottom), and I love having a physical 5-row keyboard... but I guess I am in the minority! I also wish they would bring back the Green/Red Answer/Hangup buttons. Nothing is worse then when your hands are wet or something, so your damn touchscreen wont let you drag to answer a call and it goes to VM.
I think people choose form over function too much. Physical buttons are so much better than capacitive, as is a slide-out-keyboard in exchange for a slightly thicker phone. If a quad-core slider existed I would give up on the HTC One in a second, but I don't see it happening any time in the near future, and although my SK4G is still the most ergonomically pleasing phone I have ever used (with the original T-Mobile G1 a distant second), the buggy OS is still stuck on Froyo so I need a new phone and can wait no longer.
MT button: I can't say I ever use it. Back or Home gets me to the desktop, then I click on which app I want. All my "multi-tasking" groups are on a desktop page together, so why would I want a seperate MT screen where the order of which app I want constantly changes? On my SK4G I hacked the MT button to be a search button instead. Home/Search/Back/Menu/Answer/Hangup... those are all the keys I want, and I want Volume Up/Down to double as RightArrow/LeftArrow when typing. ...plus a slide out 5-row.
The MT button isn't even a true task-switcher/closer as it should be... it is just an app-launch history that you can clear things from. The whole system just seems like a lie to me. People think they are closing down apps by swiping them away, and they should be, but they are not. If an app gets launched by another app or on startup it doesn't even get added to the list... and the list always confuses me as I wish it was sorted in the opposite direction. An MT button would be great if it functioned like Windows TaskManager, but until then, I have no use for it.