As Yippie said, it should be more about what you enjoy playing, because
a) This chronicle is quite balanced, it's not like Interlude where only archers and nukers were relevant in PvP... You can make basically anything work here, and
b) Fastest way of leveling up is via the RBs in EU prime time. To RB parties, basically anyone gets invited except for nukers and usually healers (because on low lvls, healing is usually done by summoners due to their unlimited MP).
Chars I probably wouldn't suggest right now are:
1) sorc and sps because a) they are without a question slowest exping chars right now and b) they have basically nowhere to farm on high level. SPH/necro are so-so because at least they have CDL for normal farm, but it's still bad compared to RB parties.
2) Daggers I'd only pick if you really enjoy playing them, they got a boost in this update but I don't feel like it did much to them. They're not necessarily bad, but you really need to know how to play them.
3) EE/SE are basically just buffers/rechargers right now, because bishop got Chain Heal while other two didn't, which means they're virtually obsolete as healers.
4) Temple Knight is, well, Temple Knight. Not much has changed since 2002. At least now with regular RB parties they level up as quickly as other chars.
5) WC/PP as a main... I've seen a lot of people do it, so it's possible, but it's pretty hardcore.
If you really just want a specific suggestion, for 2 windows I'd say Tyrant + WC. If you ask why WC and not PP, here's why (also yes, PoWi and PoWa are equeally bad):
Prophecy of Fire
1
buff
72
0
8000000
400
-
For 10 min., party member's Max HP +10%, HP Recovery Bonus +10%, P. Atk. +10%, P. Def. +10%, Atk. Spd. +5%, Debuff Resistance +10%. Consumes 10 Spirit Ore.
Chant of Victory
1
buff
284
0
6700000
-1
-
For 10 min., party member's HP/ MP Recovery Rate +20%, P./ M. Accuracy +4, P./ M. Evasion +4, P./ M. Atk. +15%, Atk. Spd./ Casting Spd. +10%, P./ M. Critical Rate +15%, P./ M. Critical Damage +15%. Consumes 30 Spirit Ores.