This is my Modern R/W Turn 3 Allies deck. i have been fine tuning and testing this deck for almost 2 years and this is what it has come to...
Each creature in the deck is a ally which is going to make all of there abilities trigger on enter, including the ally that enters from captain's claw, all of your allies can get, haste, menace, vigilance, +1/+0, protection from colors, lifelink, and straight life gain from Ondu Cleric.
Aether Vial is in the deck to spit out allies for free every turn, its also a good way to get around cast triggers and counters, Aether Vial never needs to go above 3, so keep it on 1 or 2 while you need it and 3 to cast the higher drop creatures.
Ally Encampment is pretty obvious, you can get extra ETB triggers later in the game with the ability to return allies to your hand when you have extra lands, you could probably replace these with Cavern of Souls aswell, i do think Cavern of Souls belongs in the deck but in my opinion your going to be pumping out allies so fast they wolnt be able to counter them all.
For a turn 3 kill:
Turn 1: Land (white source) + Hada Freeblade
Turn 2: Land (red source) + Akoum Battlesinger
Combat, Swing both Akoum Battlesinger
+
Hada Freeblade
for 5 damage
Turn 3: Land + Expedition Envoy + Reckless Bushwhacker
for Surge cost
Combat, swing all 4 for 19 damage and kill.
While Hada Freeblade is out. All of your other creatures are triggering his ability giving him 4 total counter, making him a 4/5. 2 Akoum Battlesinger triggers from Expedition Envoy and Reckless Bushwhacker making hada freeblade 6/5, and Akoum Battlesinger 3/1. Expedition Envoy gets 2 Akoum Battlesinger triggers from itself and Reckless Bushwhacker making him a 4/1. Reckless Bushwhacker cast for surge gives all other creatures you control +1/+0 and haste, making Hada Freeblade 7/5, Akoum Battlesinger 4/1, Expedition Envoy 5/1, and Reckless Bushwhacker gets a Akoum Battlesinger trigger making him a 3/1, swinging with all 4 for a total of 19 damage.