I like different things about each band.
For studio records and overall musical output, Priest edges out Maiden slightly. They had a bit more variety and their streak from the 70s through the 80s is unreal. Also, Unleashed In The East is an unparalleled classic. Maiden of course had incredible albums in the 80’s and did some really ambitious stuff but I tend to get tired of them a little sooner.
Iron Maiden is the better live band I think. They’re all in great shape and they’ve always had fantastic stage sets. Judas Priest have some deadly live (US Fest 1983!!!) stuff but I feel Maiden has upheld a high standard of quality much longer.
In terms of attitude and vibe I really dig Maiden. I like their punk rock “fuck you we’re gonna do things our way and make a mockery of what you think we should be” ethos. And Bruce is an interesting character.