Should I go for PPC monetization of a forum website or go for 1-2 affiliate products? which will work better? or better do CPM?
None of the above. Affiliate marketing works only if you do it the right way. Most people do the wrong way...meaning sending your marketing money to send traffic to the vendor who gets your customers.
One of the most important things people seem to not ask themselves is, "Which option is better for my niche?" If your forum is in a niche that does not monetize well for affiliate products, then maybe PPC is your best bet. If you are running a forum about payday loans, you should probably promote payday loan affiliate offers. Just an example.
Hi: See which one works best for you and your niche. Try both and decide based on results. Good luck, Dan