Well I think both are good.
Maybe try it on a P-Server first before official Aion Server?
1. Gladiator is good because he is strong against monster and can fight good alone (pve).
PvP also good. His Skins are nice (weapon, armor,..). (same as a templer)
2. Templer is good too. He isn´t that strong like a gladiator but can put in much damage.
He is a Tank and good for every instanz (you are requestet as a tank
)
But he dont do much damage. Thats qhy you need much Krit in youre equip.
Yust try it out.