I've only shot in the studio with the HVX200, but have had more experience with the XL-H1 than I care to share (I also own the XH-A1, the H1's little brother).
The HVX is a solidly built, but the recording medium kills me. The P2 files are huge, which would be great if they were truly HD. However, the HVX's sensors are only 960x540 and they use pixel shifting to achieve "720p". The XL-H1, though heavily compressed, has sensors that are 1440x1080 ...still not true HD, but at least you have the option of taking the HD-SDI line straight to a tower and record the signal at 1.485Gb/s.
In terms of image quality, neither are really ideal. I'll take HDV over P2 for storage reasons alone.
A better question, though, is why aren't you considering the Sony EX1? It is cheaper than the XL-H1, has full 1920x1080 raster, 1/2" sensors, records at 1080p, can under/overcrank from 2-60fps (I think) at 720p (same as HVX), has a killer Fujinon lens, solid state media records at 35mb/s, etc. My school is preferring the EX1 over our Sony F900 because of its full HD raster (the F900 is only 1440x1080 as well).
As a side note, Canon's 24f mode is actually pretty good. The kicker is that it is proprietary to Canon's HDV cameras. Once I stomached that, I was pretty pleased with its performance. There is about a 10-15% decrease in resolution when you take Canon's HDV from 60i to 24f, but I'm willing to lose the resolution for the gain in the look.