This is a tough one to answer b/c there is no "correct" answer as to what's best. It depends on the player.
Very few casters can also melee. A Heretic might best fit that description. Vamps have spells and the new Mauler toons have a lot of toys and hit hard, but not true spellcasting.
For pet casters, all are pretty much the same. Cabalist and Sorc for alb, Enchanter for Hib, Bonedancer or SM for Midgard. you generally want to go the highest dex race for each realms (that would be Kobold/Mid, Lurikeen/Hibernia, Saracen/Alb).
For melee, all melee toons are also similar. None are actually the best. Some are better offensively than others, while others are better defensively, or are hybrids that offer other things (paladins for instance with endo). The 3 light tanks are the most grouped, but the heavy tanks are probably easier to level up with and still good at PvE and RvR.
This is not a game for new players to easily fit in. Do you know anyone who plays this game, perhaps from another game you have played? Without some help, it is very frustrating, and for new players, it seems like a ghost town b/c very few players level up the old fashioned way. You have to have patience to learn the game and fit in, but try not to judge the game until you reach at least level 24 and can enter thidranki (can actually enter at level 20, but I recommend waiting until level 24 so you can compete more easily). DAoC is primarily played by most of its playerbase for its PvP (or RvR) content. The PvE for new players is extremely unfriendly at this age of the game.