I went from a 2008 E90 N54 to a 2011 E90 N55, and traded that in a couple months ago for a 2012 335is. I love the N54 motor and its tune-ability.
The N55 will probably come along soon though.
2008 335xi E90 Alpine White - Sold - 8/19/10
> 2011 335xi E90 Jet Black - Sold - 6/27/12 > 2012 335IS E92 Crimson Red - Current