I’ve only been to Rainy, so can’t speak to fishing but here’s what I like for sites.
Dock sites are king, sand sites are OK if you don’t mind getting wet, rock sites are rock and not very pleasant to get in/out of. I’d look at the NPS site instead for searching campsites, halfway down this page is a nice interactive map, which links through to the recreation.gov page for each campsite.
We’ve been picky about where we’ve stayed based on site layout, landing type, and wind direction, some can be quite exposed to sun/wind and/or have a big hike up from the lake. Hope this helps, good luck.