Here's another vote for the Federal shells with Flite Control wads, they sure make some nice tight groups with OO buck out of my cyl. bore 590.
If I were after deer and could only use buckshot I'd use Dixie Tri-Ball (3- .60 cal. balls @ 300+ grains each). Legally they're still considered buckshot.
They only come in 3" + 3.5" though.
If it were legal, my first choice would also be slugs.