No brainer: definitely a BLU!
The screen is miles better (brighter, crisper, less washed-out) for a very limited amount of extra cash, and it's fast enough in most cases knowing that overclocking limits are a bit of a lottery.
I had both: my FLU overclocked only to around 150 when the screen front light was OFF, and pretty much never beyond 133 with the front light ON (and it was always on to see anything). Plus the little handmade FLU switch at the back of the console is not that slick (compared to the "hold select button for 5sec" on BLU) and got stuck in most cover cases as it's sticking out at the back.
My BLU goes up to 166+, unfortunately not much higher with most apps... still better than my FLU though, but I might have been unlucky.
Like I said, just for the screen: BLU rules.
JBB