JPEG Vs. TIFF Quality for Zenfolio?

[Daniel Browning]

I was wondering if anyone knows the best quality to post pictures on Zenfolio.com for large prints.

Well, TIFF is best quality, but the difference is so minute under most circumstances that it's not worth the extra time. Compared to the highest quality JPEG, the only possible difference you could see is slightly higher detail/contrast in high frequency chroma detail (e.g. red feathers the size of one pixel). For most purposes, even the highest quality JPEG settings is overkill; more middle-of-the-road settings give "good enough" results.

Sometimes my images are cropped mildly.

For any given file size, compression is better than cropping, unless the software is braindamaged somewhere (e.g. uses a point-sampling resize).

If I use TIFF, should I use 8bit or 16bit?

I don't know of any printing services that can benefit from 16-bit files (certainly not MPIX); they would convert to 8-bit anyway.