I've never gone to a national Alpha Phi Omega convention, but I have been to a sectional convention (at Purdue) and a regional convention at IU.
I had a great time at both of them...it was great to meet brothers from other chapters. (I actually briefly dated a brother from Michigan whom I met at regionals!) The best part was singing the toast song at the banquet at regionals...we had this gigantic circle going through a couple rooms...and to hear everyone joining in...it gave me chills.