I second Lordanmol's question: it depends on what features you need. There is no "better" phone among those you cited. They only have more or less business or non-business related features.
There are people who would hate the P910 because it isn't built to mainly be an MP3 walkman (even though it can do that as well, but it's not its main focus). Others would hate the 6280 because it's not so comfortable to use as an organizer, not having a full keyboard...
So, the key question is: do you need a full-featured portable business tool with a well-working organizer, or do you prefer a trendy cell phone which isn't too bulky to be carried around? Pick the P910 if it's the former, or the 6280 if it's the latter.
Honestly, the features on the 6280 and 6270 are more suited to me and I dont actually need an organizer. Yesterday I checked with a local mobile store about the 6280 and they said that Nokia has withdrawn the product due to large number of complaints. However they aren't sure what exactly the problem is.
Besides, I checked CNet.com and the reviews about the 6280 were'nt great at all. Lots of complaints about the phone hanging up. Infact, the 6270 has better reviews and had a better ranking as well. Personally, I like the 6280 better and had planned to pick it up. But now those bad reviews and the numerous glitches have thoroughly confused me. I live in Dubai and the local stores here aren't really promoting the 6280.