I haven't used Ucross but I was tossing up between the two mods for a while.
Better combat enhanced is very well thought out and adds a level of depth to W3 that I cannot play without. As thibaudv said, it changes the game mechanics in at way that forces you to use everything at your disposal, consider every engagement, and actually think. One slip up on death march can mean your death but as you become more powerful, you have many more tools at your disposal to mitigate the punishment for mistakes.
BCE makes the game extremely dynamic. I don't 'specialise' because of it. Having a well rounded character not only works best, but is a lot of fun and really allows you to role play Geralt. I recommend getting the
instant sign casting mod or if you use a game pad, get one of the relevant instant sign casting for gampad (I use
this one for DS4 but the touchpannel macros are broken at the moment since patch 1.07 - no biggy, the main controls still work a treat)