what's to decide? these are totally different bikes. the crf is an MX weapon while the EXC is a high performance off road machine. if you're going to ride mostly trails, get the exc. its a no brainer. that $1300 price difference with vaporize once you start changing the CRF to a more off-road type bike (i'm assuming the KTM is $1300 more). the crf will have a small gas tank, MX suspension, and tall gears (1st and 2nd anyway). and do the even come with a kick-stand?
also, being the owner/operator of a 2 stroke its easy to say that the E-start is no big deal. it is a very, very nice feature (but i'd still spring for the addition of a kick-starter).
as long as you're going 4 stroke, why not the 525 EXC? same weight, more power.
hope this helps
jeremiah