I'm replacing screws on a pool cage now (rusted steel hex-head screws in hollow aluminum posts). A torch makes the biggest difference. After doing the first hundred or so, I now just heat them all before even attempting removal so I can start with a non-stripped screw head. Fortunately, the ones that don't come out I can just drill through in most cases, though some are unreachable with a drill, even with one of those 90 degree tools.
If you're attempting to use an easy-out, forget the drill bit(s) that come with it and just buy cobalt bits. Same goes for drilling out a hopeless screw or bolt.