I opted for no nav in my car -- at the time I was shopping for my car it was actually fairly difficult to find one without iDrive.
I think the interior looks more classic, sleek and un-fussy without the idrive screen, but that's just my personal preference. I have a Garmin and Google maps if I ever need navigation (which is rarely), and my other car has nav.
I have had a few service loaners that all had iDrive and I didn't hate it, but I found the interface to be a little unintuitive. Probably something that's easy to get used to once you have it for a while, but as a general rule I will almost always pick a car without a huge screen in the middle of the dash if given the choice.
2008 E90 335i // Black Everything // photos
COBB tuned / QTP e-cutouts / Helix FMIC / cp-e DCI / AWE BOVs / Black M6 wheels + Toyo Proxes
(and yes, I am a girl)