I usually go with what I enjoy running. But the following have become important over the years:
- Mfg support - do they update necessary parts that require attention in a reasonable time
- Cutting edge tech - is it just a revision of a 5 year old kit or is it new and cutting edge
- Online end user experience - what do the club racers think
- Durability
- Personal experience - do I enjoy wrenching on it/ does it perform on the track in my hands/ etc
Things that don't sway me:
- Fanboyism
- Chassis of the week
- Peer pressure