I"ve used both Pioneer and the kenwood eXelon decks.
If you value looks over SQ then go pioneer because you can get a really flashy pioneer deck. If you value SQ over looks you won't be dissapointed with an eXelon deck.. they look decent sound even better, and you will definitly have a sufficiant amount of control over your system (although pioneer decks usually have a bit more).
Keep in mind that a lot of people who give opinions on products have never used them.. they go by what others say/think (you know the story).
Kenwood, in the past, has had a bad reputation for various reasons, but their eXelon decks are well worth the money IMO (most pioneers are as well). When I switched from my old pioneer p-600 to my eXelon x659 the music became clearer and more natural sounding.. but obviously it wasn't quite as flashy..
Just make sure that you choose a deck that fits your needs, and not one from a general opinion. The reason for this is because, there might be pioneer/kenwood fanatics that will praise their decks, but if the deck they reccomend doesn't meet the goals you want to achieve, there's no point in getting it.
Basically what I"m saying is that the Pioneer/Kenwood debate is useless because it is too vague... so you need to ask yourself what you want out of a head unit first before you can decide on what deck will best suit your needs.
Would I buy another eXelon in the future? yes.
Would I ever use another pioneer unit again? yes, but it would probably have to be a higher end unit for SQ reasons.