Instead of buying a cheapo 15" TFT or 19" CRT I'd put my money on a high-quality 17" CRT.
Check out the pricier versions of Sony and Samsung monitors with Trinitron screens. I don't think you'll be disappointed.
I'd never choose a TFT for an Amiga. The ability to run many different resolutions depending on what application you're using isn't really compatible with the fixed-resolution philosphy of Windows and TFT monitors. Sure, the 15" ones look great in 1024x768 but switch to 800x600 (for example in a full-screen picture viewer, a game or whatever) and it looks crap.
