I had the same dilemma and today I made my decision. I went for the V3xx, mainly because of the price. The things I was most concerned about, both phones have - MP3 player, microSD, A2DP, nice screen and an OK camera (quality is roughly on par with my Nokia 6682). When I went into the Cingular store, the KRZR was $200 with contract and rebate while the V3xx was $80 also on contract and with rebate. I also didn't like the color and finish of the KRZR all that much, but that's more of a personal preference.
I was waiting for the Nokia N75 but it won't be out for another few weeks and the pricing is likely to be much higher than this is.