Now I'm trying to find a copy to double-check, but I'm pretty sure a previous revision of TRO3050 (not the Upgrade version, but the original or the revised) in the intro to the Clan section stated that the Omni variants were tagged Prime, A, B, C, etc. based on the frequency they were seen by the IS forces during the Clan Invasion. Remember, the TRO series was initially written in-universe by Comstar, so they wouldn't necessarily have all the background info on Clan stuff and what was the favorite configuration in Clan-space. My copy to double-check is at home, not where I thought I could access it easily, I'll have to try tonight or tomorrow. So things like the Gargoyle Prime is the Prime not because the Clans found it the most useful in inter-Clan fighting, but because of how often it was seen during the Clan Invasion.
Whether the above is true, or something my memory made up, we have to consider the different ways these variants could be used, not just in a straight duel, etc. While some variants will work stellar as a duelist, the Viper is a fast, medium-weight, armed recon 'Mech.
The Prime is a generalist scout, with MPLs to handle fast movers, MGs for infantry, and SRMs for fun. The AMS helps provide cover to escape if it encounters something it'd rather leave to a starmate.
The A is an obvious over-powered duelist, able to overheat to unleash a lot of damage and then jump away.
The B is an obvious long range duelist. The SPLs and Flamer allow for some crit-seeking if absolutely necessary, but more importantly, they allow it to start fires for extra cover and slaughter any enemy infantry it stumbles across.
The C is one I believe was developed specifically for the Clan Invasion. Anticipating facing swarms of infantry and tanks, this variant works great as a scout to flush hidden units and quickly destroy those infantry units and vehicles.
The D I'm unsure about. It looks like someone took the A and decided they wanted a cooler running version that could plink at long range.
The E is the typical ATM configuration for a light/medium 'Mech, an ATM 3/6 and 2-3 tons of ammo, plus some secondary weapons. Since the weapon was new I can forgive its shortcomings, but I would have preferred dropping a ton or two of ammo and maybe an ERSL to upgrade to an ATM9. Even if it meant only having a single ton of ammo, I would have been happy with that for the shear punch of 9 HE missiles.
While the MG Arrays of the F will work for infantry, on a 'Mech like this, those are designed for critting an enemy to death. While the enemy still has most of its armor, fire the MGs individually to crit-seek. Once the armor is open in a key area (engine, ammo, Gauss, etc.) switch to linked mode for the chance to land all 4 MGs per array in the same location. This gives you a better chance to crit that key component and bring down the enemy faster.
The G is a more modern version of the C, that allows it to fight at longer ranges. I wish it could have kept the full-size Active Probe to take advantage of this range, but alas. If you compare the C and G, both have a flame-related threat for infantry, BA, and 'Mechs. Both have additional anti-infantry guns (MGs, vs APGauss), both have an Active Probe, and both have some kind of Medium Laser backup for bigger targets.
The H is similar to the A, but opts for SPLs instead of SRMs for crit-seeking. It can jump and fire the HMLs without any heat gain until a target is nice and opened up, then hit the big red fire button before jumping away to cool off.
The I config is geared more towards ground-bound fighting in my mind. By running you can fire all three HMLs most of the time, dropping one to cool off or jump away. Similar to my ideal version of the E, this one only mounts a single ton of ATM ammo. In this case I would go for either standard or ER ammo, to give it the ability to hit a target at longer ranges.
The Z is a Society version of the I, swapping for improved versions of the weapons. However, in this case I might have preferred dropping the LAMS and Light Active Probe for more iATM ammo simply for the more versatile extra ammo types.
