I know about the racial ship resits but what would you have loaded if on a pvp roam ?
Just have all the missiles in your cargo then load the one that you’ll need as the fight is starting. You usually have a lot of time before target (or you) lands from warp to load. In case you’re using rapid launchers I’d stick to thermal on first clip and set auto reload off then choose correct damage on second clip.
I would think this myself, first, like you said racial ships and their resists, so if you don’t have a good ammo type already loaded don’t bother as you are already at a disadvantage.
Most PVP is fitted for max DPS which means they most likely won’t fit any real resist tank so if you are loaded with a good damage type for that ship you are fighting try it on, however they will most likely be using combat boosters where their hole is so expect it.
Also sometimes their tank is speed, so missiles won’t hit as good, web them and I’d go with EM in that case, EM seems to be a universal weakness.
Anyway I don’t PVP so take it with a grain of salt.
Thermal if you really have no clue what to expect.
However, if there is any indication that the probability to meet a T2/T3 Caldari or Gallente enemy is raised, go for EM.
I agree with Thermal being a solid starter - but beware. There are a few hulls out there that bathe in Thermal goodness - the Wolf being one of them.
Be a smart bullet and know your hulls - at least those that resist certain dmg types very well.
If you’re using rapid lights/rapid heavies, I’d say to generally load thermal or kinetic; most of the time either of them is a reasonably safe pick against T1/navy/pirate hulls and half of the T2/3 hulls in the game (T2/3 Amarr generally have a thermal hole, while T2/3 Minmatar generally have a kinetic hole).
For anything else if you see them coming in/on to you on d-scan you should have the time to swap ammo to what’s optimal for that particular fight. If you don’t know what’s optimal then kin/therm loadings are okay if you aren’t damage-locked, like certain Caldari hulls are.
But if you’re not damage locked (note that this applies to the Hookbill; it has a larger kinetic bonus but still has great output with the other damage types) then carry a stock of all damage types- and for some also a stock of all damage types of one or both T2 ammo types (on most rocket hulls for example you’re going to be packing 12 different types of ammo; faction/Rage/Javelin of all four damage types).
Rapid launchers you generally want to load a “safe” pick for damage type because the reload time is enormously long, and you might not (probably won’t, really) have time to swap ammo before the fight starts. Anything else that 10 seconds isn’t so hugely burdensome that you can’t swap ammo before you commit.