I use the RMSSS/RMFRP (snap, normal and deliberate) modified.
We don't apply the bonus modifiers for snap or deliberate, as it is supposed the time is contiguos, we use them for 'actions ordering', I will try to explain it:
You know that we have % activity for any phase, 20% snap, 80% normal and the rest for deliberate, well then it is a good method to use that for evade initiative rolls.
Example: 2 foes want to attack, 1 have its weapon drawn and the other not, as draw weapon (with no use of skill) takes at least 20% activity, then it is clear, the attack for this one need to wait until normal phase, so the prepared one attack first with no need of initiative.
Then, the round tactical sequence is:
- Each player announce their actions, there is no need to say explicit "in snap I...int normal I...in deliberate I...", as the actions are splitted by activity automatically and there is no bonus.
- Split the actions by activity.
- Roll for initiative only when exists confrontation, like simultaneous attacks between foes, 2 attacks against the same target if the order is important (if you give XPs to the group instead by character there is no need as it is not important who kills the target, not?), it is easy determine when there is confrontation.
About actions announcement, a good example is: "I draw my weapon, run against X foe and attack it", easy, right? (with no need of "in snap...").
So, automatically, the charactern draws the weapon in snap phase, moves in normal phase and if there is enough activity attacks in normal phase too (as you need 60% activity for attack).
Another good example of this could be: "I move to X distance and cast this instantaneous spell". Well, it is an instantaneous spell, but it has limited range (or you want to be nearer for BAR), imagine that caster need to move with his 80%+ activity, although it is an instantaneous spell, he cast it in deliberate phase, so it is the last of all actions (after all attacks and others in snap or normal phases).
About spells we don't use the penalty for cast spells in snap phase (remember in this system the time is like continuous), so the same for all other is applied to spells, they takes 75%, so all other actions are made in normal (we have only 5% in normal phase) or deliberate phase.
See that an attack can takes 100% activity but if you do it at beginning, there is no need to wait until deliberate phase, so for spells is the same, there is no preference for one, all actions with the same treat.
One exception, instantaneous spells, they can be used earlier than all other actions, as it is their purpose. If you think it can give advantage, then apply it only to defense and support spells, and use initiative only for attack instantaneous spells. If you use initiative for defense instantaneous spells surely you will destroy their usefulness or purpose.