With zero external credits you're not going to be able to fight 1v1 as any archetype, at least not for a very, very long time, so you're going to want to look at which guilds can bring the most to a group fight without having to invest too much. Bards are a good choice, as you can just sit there trying not to die while your song boosts all of your allies and harms your enemies. Druids and mages are also nice because even if you can't fight too effectively you can still protect areas with a demesne or break an opposing demesne.

It doesn't take that long to earn yourself enough gold to buy credits and eventually transcend one or two skills. Gold in Lusternia is relatively easy to gain, and the in-game credit market has slightly lowered its prices.