Aaron,
What type of bass and what sort of tone goals are you after? I don't have experience with other manufactures, but I'll share what I can.
X45J1 - Deep tone humbucker - I only have experience with the bridge version of this pickup. Output seems low, bottom end and low mid punch are there without out a lot of top end. I found it easy to get the bridge jazz "burpy" tone out of it. Probably sounds great for those into a passive J bass where content above 4K to 5K is not important or necessary. When I read others comments on the Bartolini "warm, low mid bump) tone, this is the pickup I think of.
X45K - Brighter and higher output than the J's - I had a matched pair of these. The neck reminded me more of a P bass than a J (not my sound), but was definitely brighter and louder. Not quite hi-fi bright, but aggressive bright with plenty of low/low-mid punch. Back when I played rock, these through my ampeg just punched through. These are no longer offered in the catalog.
X45CBJD - Classic bass with more "air" while retaining the lows/low-mids - I'm currently testing these out with the "single" neck pickup and the MV52CBJD MM style at the bridge. Similar in output to the X45K's, a bit more refined and the top end is extended further upward with a little less aggression being played out. The neck is less P like, but I'm still not a fan of a soloed neck pickup.
I hope this helps,
Matt