When I go to the lumber yard, I don't let them pick my lumber, I pick it. I start digging in the rack and I eyeball down each and every piece. I check for crown, which is the amount of bow in the edges, and I check for twists and overall straightness. If they are not perfect, I refuse to pay the two and a half prices they are asking for them.
I always restack everything nicely. Regardless of your joinery technique, if your edges don't line up nicely, it won't work out. That takes near perfect lumber. Also, to join lumber, you need perfecly straight cuts.
Have you considered using dowels? Three or four 3/8th inch dowels, an inch to an inch and a quarter deep, spaced equally apart, and glued real well, then clamped tightly, would go a long way in making your butt joints stronger. Plus, they look nice. Coupled with some nice, straight lumber, you would have it "together." Just a thought.