Which version of Arma 2 should I buy?

[xornand 1]

I see there is

Arma 2: Operation Arrowhead

Arma 2: Combined Operations

Arma 2: British Armed Forces

Arma 2: Private Military

Arma 2: Reinforcements

Do I buy them all or does the last one released contain everything?

[sickboy 13]

Arma 2: Combined Ops

and

Arma 2: Reinforcements

So you get A2, OA, BAF and PMC.

[xornand 1]

Arma 2: Combined Ops

and

Arma 2: Reinforcements

So you get A2, OA, BAF and PMC.

k thx