I leveled as Combat and while I was able to burst down targets fairly quickly I find Watchmen having to use their OOC heals less. Either one will work well though so it's up to you.
\From the theorycrafting articles that I've read that is true. Strength gives ~.20 and Power gives ~.23 (both of those are rounded to the nearest .00). As you said, Strength also adds to Critical Chance (linearly instead of logarithmic [diminishing returns], I believe). The even bigger bonus which you didn't mention is that the bonus to strength is "double buffed." With both Force Might and Force Valor, Strength actually provides a larger average damage (which includes critical chance) than Power for any attack with a large damage Coefficient (basically all attacks with the exception of strike). Note: If I find the article again I'll link it.
That's actually great to see, if you do find the link let me know and I'll include it on the post.