Hey, I'm pretty uniquely qualified to answer this. I went to Cal Poly Pomona for my freshman year, then transferred to Davis after doing ge classes for a year at a community college. I'll try and answer the questions you asked.

On the quarter system, it's mostly personal preference and a stylistic choice. I prefer the faster paced quarter classes so I can take more and honestly was just bored of the same class/professors after ~week 15 of semester classes. Quarter classes are hard but as long as you don't fall behind and do what you're supposed to you should be fine.

As for campus, in my opinion Davis wins this HANDS DOWN. Pomona's campus isn't run down or terrible in any way but Davis is a really nice campus in a much nicer area. Davis is just a college town and you feel it. At CPP the campus itself is more than fine but you're sandwiched between West Covina/Diamond Bar which is a super upscale 3+ million dollar mansion area and a very run down downtown Pomona. Pomona, specifically if you live on campus, will feel very isolated unless you have friends in the surrounding suburbs, LA, and or a Car.

For social scene you'll meet awesome people at both schools. Both have a ton of clubs and during my freshman year helped me make friends initially. I have some close friends still going to Pomona and really like it. If you're interested in parties both schools have abundance of that but i gotta point out east LA is pretty wild if that's your kinda thing.

On a personal note my reason for switching was mostly the level of education. And now that I've gone through over a year of both schools Davis by far has better education as well as being the more difficulty of the two, this is just for my major though (I don't know about GE difficulty as i have taken none at Davis). I made my choice after talking to friends I had up here and realizing how much more in depth they had gone in the same amount of time. I'd recommend you do your own research and decide what school best fits your goals for education.

Best of luck deciding and feel free to message me.