I haven't listened to the pioneers so I can't give a straight up comparison, but I got the kb-15's and the matching center and so far I like them a lot. Not too bright and has nice midrange, very clear sounding.
When I listened to them at best buy, I couldn't get any further away than about 2-3 feet and I couldn't change the music they had playing, (I hate that!!!!) and they did sound a little too bright that close up which made me a little weary, but I really wanted to know what they sounded like with my setup and seating distance so I took a chance on them and took them home. At that price I figured it was worth a shot and worse case I'd just take'em back in a week or two. I think the best thing you could do at the current prices, is to buy them both and take back the ones you don't like.
Let your current setup and ears tell you what they like.