Roll for initiative!

Over the years I've tried various forms of initiative - per side or per individual, every round or once at the start. I experimented with various systems before stumbling upon this system which immediately stuck:

Attacks/spells are resolved one group of combatants at a time. Within each group everyone rolls a d6 and it is resolved in that order. (Ties are simultaneous).

For example, if one round A&B are fighting X and C is fighting Y then first A,B and X roll initiative and resolve their attacks in order, next C&Y roll initiative and resolve their attacks in order.

Because it is resolved in small groups, there is not a big gap between A attacking X and X attacking A, so you only need player A's attention once to cover both attacks. Hence despite rolling initiative for every character every round, it counter-intuitively goes faster. There is no book-keeping required, or counting down of initiatives. As we all sit round a table and use miniatures or counters, I just point to the group to be resolved, everyone in that group rolls a d6 and puts it next to their miniature or counter, then we remove it when it's our go.

If you make a missile attack or cast a spell at someone in a group then you are part of that group, but area attacks always go last (this seems plausible, but the true reason is because otherwise the whole combat would be one group and everyone would have to roll initiative together).

Note that this system assumes all actions for the round are declared first, and then all actions are resolved; that is, there is no initiative order for declarations. The order is simply players declare, followed by the DM. It is incumbent upon the DM to strive to be impartial.