I've got plenty of experience ofn XP2 and BW400CN, none on the Fuji though. Fuji is cheapes, XP2 dearest.
BW400CN is definitely smoother at box speed and takes underexposure a bit better than XP2, hwoever I haven't had the chance to overexpose it to the levels XP2 will take (ISO 50 is very useabl on XP2 and I suspect ISO25 should be doable) but you need to be able to control printing or scanning if you're going to mess with the speed ratings as you will need to apply a hefty amount of contrast to an ISO50 shot. From the labs, ISO500 I find gives a nice contrast on both, but XP2 shows more grain at this speed than BW400CN.
Here's a roll of XP2 shot variously between 50 and 800.
Here's some BW400CN between 400 and 800. The skies were all intact when scanned, I've pushed them off the edge of the histogram a bit when balancing the contrast.