As is always the way, different people have different requirements.
For myself, I use UAE because it's a very good program. However, it is not and never will be perfect.
There is a latency in the UAE engine, there has to be - it's fundamental to the way it works. And for myself the combined latency of the sound, the graphics, and the input maybe be almost imperceptible, but I still feel the difference, and that's what's most important to me.
I'm lucky in as much as I have both a powerful WinUAE setup and also a beefed-up A4000 (CSPPC 060), but I can tell you I only really enjoy using one of them, even though they're both controlled by the same mouse/keyboard/monitor, and it's not the UAE.