Its subjective, the best ROM for you might not be the Best ROM for someone else, same goes with kernels.
This is because everyone uses the phone in different ways and not all phones are made equal (eg some can overclock more than others). Therefore its pretty useless to ask which is the best ROM or which ROMs should you try because people are going to tell you what works best for them, the only way to find the best ROM for you is to try a few and see which one you like best.
As for sensation and xe. The XE actually is not overclocked, the XE just runs the qualcom CPU chip at its stock speed (1.5GHz) whereas the sensation is actually underclocked to 1.2GHz. The other hardware differences is the red LED and speaker grill instead of grey/white.
Software differences, the XE has a beats wallpaper, no dice app and 2 values changed in the code of ext.jar and widget.jar in the method of get_PyramidLE_flag, it returns a value of 0x1 (true) whereas the normal sensation returns a value of 0x0 (false).
If your woundering about beats audio, its just an EQ profile, nothing special and its not exclusive to the XE either because if you replace the ext.jar and widget.jar files on a sensation ROM with the ones from an XE ROM, HTC music app will let you have beats audio effect even on normal sensation