There are enough variations that affect surface finish to keep you (and me ) confused for a long time, like conventional or climb milling, coolant lubricant, machine quality, two flute, four flute, HSS, carbide, depth of finish cut, spindle speed, material, cutters, premium quality, good quality, or sometimes acceptable quality, every one knows where these sometimes acceptable cutters come from so I won't slam them in this post but don't get caught up in the "Hey they look good, feel sharp and the prices is great" conundrum. That being said, surface finish can usually be improved by slowing down the feed and increasing the cutter diameter if possible.
You may want to take a look at M.E. Consultant, great asset for us new to machining. I use it all the time, I think it may be a bit conservative on it's results, and should be. It is freeware but I purchased his M.E. Threads for $15 just to give something back for such useful free software. M.E. Consultant can be downloaded at:
http://www.tucows.com/preview/356150.html