Sorry, but in case you guys haven't noticed, the e60 M5 shares exactly the same body as any other normal e60, save for big wheels (easily tacked on), that ///M side vent thing, four tail pipes and body kit. It hardly qualifies as a "new" looking car. Ditto with the M6/6-series. Hence, saying you think the M6/M5 (or 645ci) is the best looking BMW ever is similar to saying that the 5 or 6-series is your choice.
While the new 5 and 6 are indeed rather fine looking vehicles, my personal opinion is that the e46 M3 (hahaha!) is THE most beautiful BMW of all time. A sentiment that is echoed by many designers world-wide. Not to mention, the e46 M3 together with the e30 M3, were the only ///M cars in general production whose mechanicals defined their outward apperance. Something about the proportions being perfect (with 19" wheels) and all. To me, it's just... gorgeous. Just gorgeous!