My first iPad (iPad 2) had a black bezel, and my second one (Air 2) had a white one. The white one was actually an "accident" (impulsively ordered the silver model and figured that it would have a black bezel like the silver iPad 2). When it arrived, I was disappointed and certain that I would send it back after the weekend. Since it was here, though, I decided to give it a try. By the end of the weekend, I had started to like it and kept it. That was pretty surprising to me as I had never thought I could possibly get used to a white bezel (all previous devices had black bezels or frames).
Fast forward two and a half years: I bought a 2nd gen 12.9" iPad Pro and it also has a white bezel, this time by choice.
It's not so much for aesthetic reasons, though, but practical ones: I use the Pro, just like the Air 2, mostly for writing texts in iA Writer, Google Docs, and my employer's light-themed support system), browsing the web, and (in case of the Pro) for sketching. I also work in a light-colored room. mostly during day time. With this usage and in this environment, a white bezel causes less strain on the eyes than a black bezel would (stark contrast causes eye fatigue), and since my eyes are already worse than I'd like, I try to avoid the extra stress on them.
If I worked in a dark-ish room with dark-ish walls and floors, chiefly watched movies, or wrote at night (with a dark background and light text), I'd prefer a black bezel, although the white bezel doesn't cause much contrast in a low light conditions, either. I do feel that a black bezel makes the screen pop more, but that's precisely what I don't want when I stare at it for prolonged periods of time.
The Apple white also looks nicer (to me) than the typical plastic white. It never looked good to me in photos or in videos, but in real life it's actually an attractive color.