I just jotted these up out of boredom at work. I think with either one of these would make Summoner/AA more than effective, easily passing Bard/AA and competing with Fighter/AA.
Mount Eidolon
NG Large Quadruped Outsider
Init +3; Senses darkvision 60 ft.; Perception +9
AC 24, touch 12, flat-footed 21 (+3 Dex, +12 natural, -1 size)
hp ~60 (6d10+30)
Fort +9, Ref +8, Will +4
Speed 40 ft., fly 60 ft. (average)
Melee Bite +13 (1d8+10)
Space 10 ft.; Reach 10 ft.
Str 25, Dex 16, Con 18, Int 7, Wis 10, Cha 11
Base Atk +6; CMB +14; CMD 27
Feats Run, Toughness, Iron Will
Skills Acrobatics +12, Perception +9, Fly +10, Intimidate +9
Special Abilities link, share spells, Evasion, Devotion
Evolutions(11) bite(free), limbs(legs, free), large(4),
flight(wings, 4), ride(2), Improved Natural Armor(1)
"Hit-and-Run" Eidolon
NG Medium Quadruped Outsider
Init +4; Senses darkvision 60 ft.; Perception +9
AC 22, touch 14, flat-footed 18 (+4 Dex, +8 natural)
hp ~35 (6d10+5)
Fort +6, Ref +9, Will +2
Speed 40 ft., climb 40 ft.
Melee Bite +12 (1d8+9 plus 1d6 electricity)
Space 5 ft.; Reach 5 ft. (10 ft. with bite)
Str 22, Dex 18, Con 13, Int 7, Wis 10, Cha 11
Base Atk +6; CMB +12; CMD 26
Feats Dodge, Mobility, Spring Attack
Skills Acrobatics +13, Perception +9, Stealth +13, Survival +9
Special Abilities link, share spells, Evasion, Devotion
Evolutions(11) bite(free), limbs(legs, free), Improved damage(bite, 1),
Magic Attacks(1), Reach(bite, 1), Climb(1), Scent(1),
Energy Attacks(electricity, 2), Ability Increase(Strength, 4)
It may be worth to take an extra level of Summoner to get Vital Strike for the "Hit-and-Run" Eidolon. Like I said I jotted them up quick at work, if you see anything wrong, please correct me.