Naming "Angel" as your favorite Hendrix song is a little like saying that Paul McCartney is your favorite Beatle. It's not as popular as John or "Purple Haze," nor is it as cool as George or "1983... (A Merman I Should Turn to Be)." But judging on songcraft alone, it stands above the rest.
Why is that? There's nothing particularly flashy about it, which might be why Jimi never released it in his lifetime. But for an artist whose songs are pretty much universally loved, Hendrix never seems to get enough credit as a composer. Sure, everyone admirers the guitar playing, but he also had an impeccable sense of melody, knowing when to use a good, subtle progression and give it breathing room, the way that he does here. Jeff Beck would have probably gussied it up until it was lost in a nine-minute jam, and Clapton would need outside songwriting help to come up with anything like it. If I believed in angels, I'd thank them that Jimi gave this song the structure and lyrics that it deserves.
Something about this magic little song transcends arrangements and performances. I love the orchestrated version, performed here by Gil Evans' band in the 70s.
Fiona Apple's rendition on MTV Unplugged is as lovely as anything I can think of (starts around 10:43).
Even Rod Stewart and the Faces could stop being silly on Top of the Pops long enough to show some reverence.
Songs usually don't get covered this often unless a) Everyone likes them, and/or b) People assume they can sing it better than the original performer (see "Blowin' in the Wind" or "Hallelujah.") With "Angel," I wonder if it's a little of both--people like it, and most people think of Jimi as the Guitar God and leave it at that. But most likely, Hendrix just created a mood that everyone wants to be a part of. Fly on, my sweet angel.