I've owned all three brands and can tell you my experience with them.
Hartke KB15: Was intrigued by the lightweight kickback design and bought one. Played one show and was in love! It was super loud and I could hear myself (amp) over the whole band with monitors. Was extremely impressed...... then the speaker developed a horrible rattle sound. I tightened the screws, but the rattle remained. I had
Sweetwater send me another one and it did the same thing. I ended up replacing the speaker with an Eminence CB15, but it made the combo around 55lbs! Also the fan of the KB15 is really loud! Overall I would never buy another one.
Fender Rumble 500 combo: I've owned multiple Rumble 500 combos and they have been very nice. The are light and loud. The only problem I've had with some that I've owned was QC issues like a fuzz sound coming through the speakers. However when I got a good unit, it was great! Had to put mine on a stand during gigs, but it sounded really good.
Ampeg RB100: I really loved this combo. It was built like an absolute tank, but I wasn't a fan of the tone. Plus at 100 watts it really wasn't loud enough to play with a full band, but that not really what it was meant for.
My favorite overall combo amp that I would buy again is the
Bugera BXD15A. I had the chance to pair one of these against a Rumble 500 and a Markbass CMD151P at a gig. The Markbass was the best, but the Bugera was a close second place and easily beat the Rumble 500. I played hard and the Bugera never farted out and stayed loud and clear. The Rumble was farting out at higher volumes. The kickback feature is awesome and I could hear myself loud and clear with the Bugera. I assume the all aluminum speaker has something to do with it. The Bugera is heavier than all the stock combos that I've owned and carpeted, but it was the best combo I've ever owned.
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