I've used both amps. Actually, went from a Jello 300/4 to a PA BB175.4B and back. (I am currently looking at other options, because I am going from a 2-way active system to 2.1-way active and thus need 5 channels of amp. Neither one will fit in my intended space with a subwoofer amp as well.)
As far as "sound quality," there was no difference between the two, beyond any possible gains that may be gleaned from the Jello's more flexible on-board crossover. Neither one was a high-noise device, and they had the same frequency response by my indirect measurements (of the system, not just the amp). By the same token, I cannot say that the PA was perceptibly the slightest bit more powerful, despite the disparity in the ratings. (Note that I use all nominally 8Ω drivers.)
Why did I switch back to the JL, then? One of the terminals in my PA managed to strip itself after some time in the install. (The terminal threads, not the screw.) Yes, it's an easy fix, but not as easy as just changing the amp out! //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif That said, my 300/4 also had a build-quality flaw. The original terminal screws were too soft, and the Phillips heads were easy to strip. Jello realized the problem and sent me out their newer, better hex-head screws. Overall, there's no question in my mind that top-to-bottom the Jello is the better-built device, though considering I paid a couple multiples of what I paid for the 175.4 for the 300/4 and Jello is a solid company, that should not be a shock. I doubt a decade hence you'll see many 175.4's, but 300/4's will be all over the place just as PPI Art Series and older McIntosh amps, etc., are scarcely less common today than they were in 2000 or even 1995. Still, I would say that unless the crossover of the Jello, which is superior to that of the PA in every way, offering greater range of adjustment and a choice between 2d- or 4th- order slopes, is a factor for your install, then ultimately just pick the one that, for whatever reason, you "like" better.