i was going to say it was a no-brainer, but decided to do some homework before shooting my mouth off. Anyway, i did some homework and here are what i think are the key differences:
- EOS 30V has ECF with diopter. EOS 3 has not diopter, which was a real pain for me. Unless you have perfect eyesight, the diop is, IMO, quite important. Esp if you ever use manual focus.
- 30V has no spot meter. This is another (again IMO) very impt feature.
- 30V has ETTL II, the new whiz-bang flash algo that uses subject distance. Canon's flash tends to be a little 'all over the shop' in tricky conditions, so this may prove a worthwhile upgrade.
- 30V has focus-assist, though it is the irritating white one, not the red one. i didn't check, but i believe EOS 3 has greater AF sensitivity without assist. 30V range is 1-18EV. If you AF-assist, using a red light from an external flash is a better idea - doesn't irritate your subjects. If you don't AF-assist, the EOS 3 is the better camera.
- 30V claims (according to Canon Museum) "predictive AF performance equivalent to Canon’s flagship 35mm AF SLR-model EOS-1V", and that its "eye-control function realizes a reduction in response time of approximately 15% compared with the high-end EOS-3, distinguishing the model as the fastest eye-controlled camera in the EOS series." i found the ECF in the EOS 3 to be a joke, but i wear specs, and some folks swear by it (the ECF, not the specs).
i don't think the other differences are impt - fps, etc. One thing not mentioned though: the EOS 3 is pro-build. While the 30V would come with a one year warranty, i think the EOS 3 will last longer and go through more punishing conditions, plus holding a better resale value.
i think you should stick to your 1V unless you're dying to try ECF.