New alt - Advice for what to play

[Foxplay]

If you want dps for groups Id go...

Rogue - dirt cheap class, they can move around relatively freely and get to groups easily. Groups always want more rogues

Monk - Can also be done super cheap (don't let the heavy amount of monk twinks on p99 fool you) added benefit of being a puller and can solo a lot better than a rogue

Mage - Will get groups way more often than a wizard... people are hesitant to group with wizards because they run out of gas... p99 is somewhat different in classic in that groups and players focus on constantly pulling mobs not just camping 1 specific room or a few spawns and waiting for respawns... thus running out of gas is a huge weakness for wizards in group situations. Mage does not have this weakness as long as they press pet attack they always do good dps

Necro - to the same extent as Mage but your pet is slightly weaker and your dots are not as relevant as the mage burst nukes in group situations. Can still be super valuable to groups but some groups may prefer upfront dps before considering a Necro. That being said Necromancers are significantly better at soloing than the rest of the classes you mentioned