I was having exactly this dilemma few months back and went for the CP88 6" in Nickel. I've only spent limited time with it as strictly speaking it's an xmas pressie from my wife, but I can honestly say I'm delighted with it. The quality of build and finish are second to none.

The other pistol I nearly went for was the Umarex Colt 1911 CQB. It's available in both black and desert sand. The reason I didn't go for it in the end was that as BB it lacked any real accuracy so would only be good for a bit of fun as opposed to actually hitting the things smaller than tin cans. Also on the examples I saw in shops the paint was already coming off, particularly on the triggers which I found quite shocking but seems to be a bit of a theme with some BB guns.

as a post script, I should add that I've since been out and bought a mini UZI so I've also got something when all I want is a bit of a blast, so it really depends what you want from the gun.