No 50cal armed plane is best for bomber busting. 190s are... okay... but the MG151s truly lack in hitting power. I unloaded my entire 500 rounds of 20mm from a 190F-8 into a single lancaster, and i'm not kidding -- he wasn't even smoking. Somebody else got the kill.
You can do it in anything with 2x20mm, but it's best if there are 4x20mm. Faster is better so you can overtake and reposition as you desire. Probably one of the best is the typh (speed and guns) but I've had some success with the Ta152 (2x20mm 1x30mm) and the chog (adequate speed, good firepower). Those are the "best" for it
That being said, anything with 20mms will do, as long as you're fast enough to get in, fire guns, and get out. Ki84 suffers in this area because it's slow, for example.
You want the BEST angle? Well, slightly high and dead ahead. But that angle is hard to get. If you land it you get an instant cockpit shot and POOF. Realistically? Oh, I'd say extreme high/low shots are best, but extreme high shots are harder to shoot back for the bombers and easier for you to get away (you're faster), but naturally that's if you have the alt to begin with.