It would help to know what you mean by best sounding, as sound is subjective. Do you want it to have elements of that tube sound, or SS?
The PF heads sound pretty damn good for their price point. There's elements of preamp tube warmth to them, and they sit very well in a mix. My biggest gripe with them, is that in direct comparisons, the PF's sound like they have an hpf on at all times. In defense of the PF though, it feels shelved at an appropriate point where the bass starts to get arguably muddy.
The 7pro has even more of that tube sound. The knobs are less sensitive, and produce a smoother gradient in tone as opposed to the PF's, which feel more sensetive in comparison. The hpf feel isn't apparent with the 7pro.
B-series heads (B, B2, B2re, etc...)feel very bass and low mid heavy to my ears, and have very little traces of tube warmth. They aren't as articulate or glassy as other heads of the time, but have a well defined low mid presence, and tight bass. They also come from a period when I felt Ampeg power ratings in relation to volume was at its weakest compared to other brands.
The 3pro, is the best sounding Ampeg hybrid compared to the svt cl tone to my ears. I do think it still suffers from that low volume era though. Unfortunately the examples I've come across are usually trashed by idiots tube swapping and self-biasing that had no business opening up the amp.
This was just a small list of what I'm familiar with and what's most common in my area. There's others like the 4pro, 6pro, 5pro, B500, etc.
I'm sure others have varying and contradictory opinions of these amps but i did my best to provide some objective comments based on my experiences with them. Best of luck with your search!
