Swiss can force some (maybe all now?) PAL games into 480p but some may have glitches.
Of course, Swiss is improved all the time, so it may only be a trivial amount of games that now have issues running at 480p.
As for your question, it depends on your target display and your definition of “improve”. If your only criteria is reducing input lag, OSSCs deinterlacer is the fastest possible. Generally though, you will get better picture quality by using passthrough and your displays deinterlacer.