This was already mentioned here, and I can't believe I never brought it up before. Clean!!!!!!!!!!!!!!!!!!!!! aluminum MIG hates contamination. We actually clean all our parts in a vapor degreaser before welding to remove all contamination and oils. You will not believe the difference this makes. I would imagine a home user could get by with brake cleaner or alcohol. This cleaning made the go/no go difference for our process here.
Also, FWIW your bead doesn't look "that" wide to me, but it's hard to get perspective. If you're already that far along you'll be a champ in no time, practice is key. Regarding TIG, you can't beat it for "pretty" and really for uniform strength either. It's simply incredibly slow by comparison and much less handy. Try filling largish gaps with AL TIG, good luck. But with a snug fit TIG is a joy, hell it's fun! Choices choices
Oh yea, Rick mentioned wire feed. This IS a biggie. If you can afford it (not that bad) a spool feeder is golden.