Your choice is between really good (5.4) and even supposed to be better (5.0). There is nothing wrong with either engine. The 5.0 is a little lighter and more fuel efficient. The 5.0 revs higher (which means nearly nothing in a truck).
Some parts of the 5.0 look like they were intended for a high RPM screamer and, well, they are. It is too early to know, but the 5.4 might have a better shot at making 300,000+ if you plan on keeping it that long.
Another part of the equation is the transmission. The 2011 6 speed has some improvements in both hardware and software which should result in it being smoother and ever so slightly more efficient.
The 2011 has the cool 4.2 inch trip computer on the dash, if you are into that sort of thing (I am
The trade off is an extra bit of incentive money on the 2010, or another mile or two per gallon on the 5.0.