This is a fairly commonly asked question, with varied answers. The first question to you is do you have any riding skill, if so whats your riding level?
Both bikes you have outlined are great, but to someone like myself a bike that size i would soon become bored with power wise. The 160 is indeed a tried and proven engine here with most people jumping to recomend it.
Another thing is, what particular bike you looking at? the 140 and 160 actually comes in a crf50 style and a crf70 style (Dpro's being the 50 style and Outlaws being the 70 style)
If you use the search function (link below) you will find a few more threads the same and if needed you can compare the advice/post's between them all.
I like the outlaws my mate has a 140 I've been riding that couldn't hurt to have more power I was just wondering what most people ride, I'm coming for the ride next Sunday at mx central, how big is the power difference cheers Sam