Eight seconds of searching would reveal several threads on this topic.  Bottom line is there is little difference today between 14#, 15#, or 16#.  Each has its own advantages and disadvantages.  14# may give you more deflection to carry the 9 pin, but you may overthrow it or leave 5-pins on shallow angles (some additional revs may offset this).  16# may drive too hard, leaving more 9-pins.  15# may do either, depending on whether you're dropping from 16# or increasing from 14#.

Throw what's comfortable.  All balls today are available in 14#-16# with the sole exception of Insite stuff.

SH

If the back ends are flyin' you'll be able to carry the 10 pin with a 14 pounder, but on most tournament conditions and on a THS with carry down you will definitely leave more soft 10's than with a 15 lb ball.

I went down to 14 pounds last year for about a month after suffering a wrist injury. I was able to still score well but did leave a lot more 9 counts and had fewer messengers, etc. After some experimentation using a 12 inch drill bit to take additinal weight out of a 15 pound ball I found that 14 pounds 9 ounces was my optimum weight in that my carry was as good as anyone else throwing a "normal" 15 pounder and my wrist could handle it without too much discomfort. Now, all my equipment is drilled down to 14.9, it seems to be the perfect compromise between a lighter weight while maintaining the hitting power under a variety of conditions.

This year my average was up 9 pins to 226 (composite 223 between 3 leagues) and I bowled the entire season with little pain.