posts wood / metal / concrete, will leave that to others...
i have 1/2" and 3/4" pipe, with some U bolts holding it all together.
one gate wants to swing open all the way
one gate wants to swing shut
i picked up a J bolt, to use as a hook, and some cheap chain, so i can hook the gates open. ( T post, current fence what ever ya got there)
i also have a couple pieces of chain in center. so when both gates are closed together. i can give one or two wraps of chain, and toss on a paddle lock.
paddle lock, it is worth getting one dipped in rubber, with cover that goes over key hole on the lock. ((keeps out a lot of dust / snow / ice that would cause lock problems))
==========
trying to get two gates that always want to natural open "CLOSED" is well a rather pain.
trying to get two gates that always want to naturally close, is also a pain.
less walking back and forth to open/close gates atleast for me, if one naturally wants to swing open, and the other wants to naturally swing close.
==========
if you go with a full gate for live stock and like. get a boat trailer jack (has a wheel vs just a piece of metal on the bottom of jack). and fasten that to the gate end. make it so much easier fighting snow / mud. just crank the jack some lift the gate and she opens, and no need to physically lift gate or drag gate, as it opens / close
i have had trouble in past with gate wanting to come off the hooks, (hooks that fasten between posts and gate), bailing wire ran around hooks and holes on gate, i don't know half dozen plus times around. it looks crummy, but its not going any were now.