we've actually found some posts that state that the negative faction is much, much lower than the positive hits, so we've been picking up writs from each and then all doing them at once. i duo'd yesterday and the two of us earned 10% guild xp in about an hour by doing one or two that we both had.
in addition, if you hail the npc several times *without* hitting accept, you may be able to get more than one at once, though this doesn't always happen, is a known bug, and may be fixed soon.
we'll end up with better faction with one or more than the others, but in the end, all 5 factions will increase, though we keep forgeting ironforge, so they'll hate us shortly if we dont start doin theirs, too :).
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EQ: Runyaessz, 5 Monk, Phinigel
EVE: Runym/Runyn/Runyl, 43M SP each
SWTOR: Pardoric, 22 Merc, on vaca
EQ: Runyariel Varyuvantel, 65 Enchanter, Tarew Marr, on vaca
LoTRO: Runyarian, 38 hunter, Vilya, on vaca
WoW: Runyarian, 70 hunter, Muradin, on sabbatical
EQ2: Runylala, 25 Troll Bard, Qey, Blackburrow, retired
WAR: Runyael, 30 DiscO Khaine, Ironfist,retired.
CoH: Hissing Chicken, 16 Scrapper, Pinnacle, retired