I have a Powerball. took me some time to get the (great) sound I have now. I (and some other people I've heard of) had problems with cutting through the band-mix with it (I think its voiced a bit scooped over all, but it can be fixed). I also plan to buy a better cab soon (most probably the horizontal ENGL 212) to further improve the sound.
the Fireball is basically a "smaller" version of the powerball, but sounds a bit different.
The Blackmore was designed to pretty much have the essentiall features of the Savage 120. I've never had the chance to try any of those 2, but they're supposed to sound great.
dont know much about the Special Edition so far, but I think I've heard, that its supposed to pretty much combine the Savage SE and the Powerball in one amp...
the ENGL-combos reallys seem to be a matter of taste, some people love them, some say they are too trebly/thin sounding, but there are also the head-versions of the combo amps (Thunder50, Screamer50) which are supposed to sound "better" with a 4*12
the Powerball has very much gain of course, what you need here (my opinion) is good EQ and good PUs (you dont have to use all that gain of course)! myself I play rythm with gain set to 12 o'clock (or a little bit higher) on channel 3 (lo gain lead), but it really depends on the PUs. I think the amp pretty much brings out the tone of your guitar.
I have 2 guitars, one has a Dimarzio X2N in bridge and the other has a Duncan Dimebucker. the X2N is a very high gain PU and it does sound good, but I ended up liking the Dimebucker much better!! less gain, but much clearer sounding and a much tighter, heavier low-end (I normally play the Duncan-equiped guitar with the Powerball)!
a lot of people use EMGs. I've never tried (active) EMGs so far, but I think they're pretty high gain, too, right? so maybe thats the problem... the high gain PUs boost the high gain of the amp even more and I can see how it easily can get too much then...