I roll for my players at the beginning of combat, using their initiative mod., that way it keeps things flowing, still leaves luck involved, and keeps the features that benefit initiative. After the rolls, I group them into separate groups that can act in any order within that group:
[ +- ] 4 man group, 1 monster example
(Player 1 and 3, roll 15 and 19)(Player 2 and 4, roll 8 and 7)(Monster rolls 13)
Player 1 and 3 would be set to group 1, Player 2 and 4 would be set to group 2. Those in group 1 would be able to act in any order within their group, so Player 3 can go before Player 1 and vice versa. The monster goes after group 1, same applies to group two; any order Player 4 before Player 2, vice versa.
Player 1
Player 3
Monster
Player 2
Player 4