which is harder?

lynxsr8

(70-270 or other ms exams) vs security+?

dubious

They're both on the easy side. If you want to compare them then look at a site like www.cramsession.com

http://www.cramsession.com/certifications/comptia/security.asp

Versus

http://www.cramsession.com/certifications/exams/windows-xp-pro.asp

CramSession puts Sec+ as the harder exam and I guess in a way it is, but again, they're both easy.

By the way Sec+ is not a 8.5/10 in difficulty, more of a 4/10 or even 3/10 with 10 being the hardest cert -- CCIE.