I don't know why everybody is saying Bard. Actually there's one reason to play a bard but I don't think it is nearly good enough. A bard brings three things: Baseline buffs, endurance chant, and speed. You can get Full baseline + specline buffs from buff NPC's from across the realm, or just buy potions, so a Bards buffs are essentially useless unless you are buffing a pet (which the buff npc's don't do). Bards also give Endurance chant, but once you are passed level 30 you can buy them for very cheap from housing (improved draught of invigoration), and never run out of endurance. They make them for pre-level 30 too but you might have a hard time buying these in housing since they aren't used too often. Finally yes a Bard brings speed, which is helpful for running those battleground XP quests over and over. But really speed is the only reason why you'd want to play a bard, apart from obviously the ability to heal, but a Bard brings no DPS so you'll have only 1 character killing anything. I think at level 23 the Bards speed becomes faster than realm hasteners, so beyond that point it will help you get around faster, but once you are there you will have a very boring time playing the Bard.
If you feel like playing a caster I would recommend a Mana Mentalist or a Mana Eld. Mana Ment can throw in a Hot (heal over time that draws no aggro) so the VW can tank a pretty serious amount of mobs at once, and the Ment can throw in regular heals too. The ment can also use DoTs to add to DPS, and use the baseline stun so that the VW can use its positional styles. And btw at level 29 the VW gets a nasty pbae damage style followup that requires using the level 10 side style first. You can expect to hit mobs for an easy 400-500 just from the proc, and its pbae. Otherwise you can use a Mana Eld and just take advantage of PBAE for lots of DPS, and the baseline stun. For example, have the VW pull a large number of mobs, eld stuns, VW uses side chain combo to draw all agro, then you should be able to get 2-3 pbae's in without being interrupted which is enough to kill yellow/oj mobs. In Leirvik I did this on a Chanter/VW combo and we could kill 6-10 mobs at a time, but sometimes you do get close to death. I guess consider that a Chanter has a baseline speed spell in addition to Pbae, and not to mention the Chanter is the most efficient PvE farmer in Hib with its pet (but this requires a Druid as well).
If you want you can play a Vamp, they are fun because they are quite effective, and while both Vamp and VW stand well on their own, nothing wrong with putting them together. If you want to play a tank as well, then I think a Champ would be ok. Champ can use str/con debuff to lower hit points and pull mobs so that the VW can side chain. Both characters have ranged insta-cast snare spell, and champ has ranged interrupts if you run into casters in the BG's.
Just play a character that you'd also like to play, for a leveling duo these days you just need some form of DPS to try and kill things fast, and heals are somewhat optional if you're playing with only 2.
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