WHO GETS THE FIRST BLOW?The initiative rules above comprise the relatively simple "Dexterity based" rules from Holmes. It leads to a situation where combat takes place in a relatively static order, with each player announcing what they do in order by Dexterity. But as I've been thinking about it, the rule could actually work better in practice than the OD&D FAQ method of simply rolling off (which was duplicated in AD&D with some complications, and without them in Moldvay).
When two figures are brought into position 10 scale feet (or less) apart they may engage in melee. The character with the highest dexterity strikes first. If the Dungeon Master does not know the dexterity of an attacking monster he rolls it on the spot. Subject to the limitation of heavy weapons the two figures exchange blows in turn until the melee is resolved. If dexterities are within 1 or 2 points of each other, a 6-sided die is rolled for each opponent, and the higher score gains initiative — first blow.
Attackers who surprise an opponent or who approach him from behind always get the first blow. Characters who are wounded continue to strike valiantly until they are killed or the melee ends in their favor, unless they choose to break off the combat and flee. If combat is broken off, the fleeing party must accept an attack without any return on his part, the attacker adding +2 to his die roll for hit probability, and the armor class of the fleeing party can not include a shield.
- Dungeons & Dragons Basic Set, Edited by J. Eric Holmes
First: there is the question of monster Dexterity scores, which can be cumbersome to deal with. But monsters already have scores which are roughly on the scale of Dexterity - simply multiplied by 10 - in their Movement rates. In fact, this is probably the biggest utility those rates will have; chases are rarer than fights and it gives fast monsters a much more significant advantage. It's also less arbitrary than rolling Dexterity for a given monster. So the rule of thumb is movement rate divided by 10.
Second: This system works best if you treat every melee as an individual conflict. Rather than simply raffling through Dexterity scores each round, the referee should note which combatant went first and proceed through each mini-melee on the field. Dexterity is only referenced, and dice only rolled for ties, when first engaging an opponent. So three fighting-men taking on four orcs will be considered three separate melees, with the fourth orc having to compare Dexterity scores with the warrior he is going up against. But if a cleric arrives and wants to go up against the fourth orc, they compare scores again.
Third: For reasons of tension and balance, I think spell-casting should always be subject to a roll-off, and being hit in a round should stop a spell from being cast for the rest of the round. So if a magic-user is trying to Sleep a group of goblins, the one who reaches him can roll off to see whether it can try to attack the M-U and disrupt his spell. This accomplishes the goal that Gygax was getting at with AD&D initiative without the enormous difficulty.
Fourth: Note the attack of opportunity in the Holmes rules. It's worth noting that this actually accomplishes everything the 3.x rules were trying to do, again with far less complication. Let's say a fighting-man is trying to guard a magic-user behind him. An orc tries to sneak by and whack the magic-user. The fighter can try to enter melee with the orc, and if his Dexterity is 12 he gets a roll-off; if it's higher he enters melee with the orc. In those cases, if the orc tries to get to the magic-user and hit him, he has withdrawn from combat with the fighter and takes an attack at -2. So this really makes guarding a character or objective a function of initiative, which makes sense. Fighting-men are guards, but if only if they're fast enough and not already engaged.
Finally: When expanding Holmes, I think one of the natural moves is to give fighting-men extra attacks at higher levels. These can be treated as if the fighting-man is in melee against two separate creatures. So if a fighting-man at 5th level with 10 Dexterity is fighting an orc (MV 120 for Dex 12) and an ogre (MV 90 for Dex 9), the orc goes before him, but he goes before the ogre each time. If he had Dex 12, he would roll off once (for him versus the orc) and always go before the ogre.
With these points in mind, I think Holmes initiative can be the most straightforward way to run initiative in classic D&D. I'd still avoid the weapon speed rules which are a crude version of what wound up in AD&D, but it's worth using initiative with the tweaks.