On paper, the spec of the BL2500s look a great deal better than the BL4s, and if I'm honest this time I do agree with these figures in pretty much any setup. As already mentioned, the BL2500s are more powerful and are therefore able to reproduce a warm and unstrained sound. These will fill a modest sized room very well as long as you don't play them very loud. These are also good value, buy a pair from Lifestyle-AV and you could almost buy 2 pairs for one pair of BL4s.
If you only really need BL4s as computer speakers or perhaps to use in a bathroom then the BL4s should do just fine and look the part too. My pair of BL2500s only look really good if I place them either side of a BS3200, so take the design concept of the BL2500s into consideration before buying.