how should i use my skimmer

Just looking to get some insight on what way to run my protein skimmer. I have a tunze 9001 running in my fluval m60 (24gallon all in one) which has seemed to be doing pretty good besides the fact that i'm getting some film on the surface in the back of my tank. It's a tight sqeeze when i put the surface skimmer attachment on but I am able to get it in there. I'm just curious what you guys would do though. Should I leave it to skim underwater and just remove the film manually, or should I surface skim since that is an option for me. What are the pros and cons for each technique.
Thanks