I am currently flying the Airbus on those Transcon routes after 6 years of flying the 757. There is no comparison. The 757 has a much greater margin as far as load and fuel capacity.
In the A321 we are seeing initial altitudes of 320 westbound out of PHL and CLT with full loads. After a couple of hours FL340 is ok and maybe 360 if you are going all the way to SAN or LAX. No way will you make CLT to SEA in a 321.
Also, you are doing TOGA T/Os almost always when full and flying over 4 hours. On the 757 we would have 190 in the back out of LAS, depart 19L (the shorter runway) with reduced thrust and fly to JFK with ORD as an alternate. Difference between 73000 lbs of fuel available vs 52500 lbs. And 40k plus per side vs maybe 30k (not really sure, actually, they are afraid to tell us the actual rate) on the 321. The Airbus is under powered, under winged and under fueled for long haul ops.
Having said that, I prefer the 321 to the 320 and 319. The enhanced aircraft are nicer, and I like the heavier feel of the 321. My landings are far better in the 321. No Airbus flies as nice as the 757, though. The 75 is my all time favorite. Convair 440 is my second.