Compared to some, I'm a relative noob in the multiplayer and have only just begun to recognize the variance in kits. Has anyone done an analysis of the better scoring kits for each class as a reference? Prompted by your comment I did a search but got nothing -- wrong search terms maybe.
Nothing so formal, I'm afraid, but the general rule is that AoE damage, CC, barriers, and taking damage onto barriers and shield wall generate tons of points while single-target damage generates far fewer. So AWs (barrier tanking + AoE) generate obscene points, Elementalists/Archers get tons, Most classes get meh, Assassins get terrible XP because they "only" assassinate priority targets, and Lego gravitates towards the bottom of the chart.
Worth noting the entire score system is rigged against Lego. For some ungodly reason, tank scoring is based on how much damage you take...and Lego's best ability means he takes 0 incoming damage. So the better the Lego player, the less XP he gets. Yeah. I know.
FTFY. It is a myth Archers get lots of exp. They do not provide additional Exp for the team, and actually reduce the overall exp potential of the team. I take a end-scorecard team centric view, as opposed to a individual kit view, because all the exp is pooled together. Unless you're a score ****** that actually cares for ME3-like meaningless vanity, it is more important to look at the two final tallies: Exp reward and time (gold per time is another derived figure that is a worthy analysis, but not mentioned here).
The four mages plus the Archer are the best kits for XP efficiency. The Lego is pretty low, possibly only above the Alchemist.
Not many people play Perilous regularly and the vast majority tend to favor completion over XP productivity. Also, many (possibly most) players are not native English users, so it is highly unlikely that you will find any info out there. Perhaps not even Bioware is aware of the difference in XP efficiency among characters.
FTFY. Archers do not provide XP efficiency without spamming KOB / KOP for the sleep support xp (and most do not, though they should).
Also added are Reaver for the War horn AoE Panic spam, and potentially Katari with Grisley mutilation (also AoE Panic), and occasionally Templar for the Wrath purge combo. These require skilled & geared players however, while mages are less demanding.
There is a limited amount of enemies, and limited amount of damage exp per enemy. Under a team view, the more players that hit the enemy, the better. Even better when support xp is triggered by the factors Shinny mentioned. Like the Assassin, Archers tend to one shot their enemies, but multiple at a time, so support xp is never triggered onto those enemies, lowering overall exp gain.
The ideal situation is support & damage exp triggered by all players onto all enemies (group mindblast comes to mind). The next best situation is AoE CC + Group Barrier spam by players that don't necessarily each hit all enemies with all players. Somewhat less useful is individual enemy CC by individual players. No CC or support xp triggered is the worst case scenario: Assassins and Archers fall into this trap.