You would want to upgrade most arcamon by using an evolution stone.
Also some event drop only arcamon are extremely good choices for every char.
Few of my picks...
Yimoogi - needs dragon evo stone to make. build its intelligence stat high and it will have extremely powerful poison (red and green). Good for bossing and pk. Good for taking lures off you. Usually quite weak though and dies quick when taking a beating from lots of mobs. Good for all classes.
Frost troll - drops in xmas event only. Like the boss its based on, has an ice AOE spell and slows mobs. I use on tao and its good for leveling. Can be quite tanky if built right.
Frost tiger - drops in xmas event only. The best pet ingame in my opinion. It has a ranged ice ball attack which blues mobs, and if built with intelligence build will basically keep mobs blue through whole encounter. Good for bossing and pk. I unfortunately have missed out on a Tiger the last 3 xmas events so im hoping to get one this year. Good for all classes.
Darkthunderzuma - needs dragon evo stone to make from red thunder zuma. I dont own one but seen them in action. Powerful multi lightning attack. Good for taos. Not having used one i expect if built right would be good for leveling potentially.
Dragonkhazard - built from khazard using dragon evo stone. If built with high intel build it paras constantly and is very fast. Very good for bossing. Useful for all classes. Khazard is also good for bossing and a viable pick of you don't have spare cash for dragon evo stone.
These are probably the main arcamon in use by most people.