I'm not sure which is better. currently I have four eight foot twin bulb fixtures with no covers in my two car garage. I do know the reason for the covers is to Disperse the light better into the room. It can get quite technical on which cover, what type of bulb, and what fixture to use. Then your ceiling height and spacing of the lights will determine what you need. along if your walls are painted and what color and gloss. If you want try and find a lighting electrical store near and stop by. Tell thing what you are trying to achieve and what youâ€â„¢re doing in there. They will be able to give you the best options and might even send a sales rep out to really determine what you need. I work maintenance for a school dist. So Iâ€â„¢m in contact with my lighting co. quite a bit. I asked them about my garage, saying I want it brighter than what I have. They said I could go High output fixtures with full spectrum bulbs. The high output would be 95 or 105 watts compared to 40 you usually see at Home Depot. The full spectrum enables you to see colors in their truer form without that yellow hue giving off by other bulbs.
Hope this helps,
Chubs