Well I have found SAM to be very boring in dungeons under level 40. There are only like 3 skills for you to use. SAM is also a close range DPS so you will have to learn more about running away fron AOEs and stuff and placement behind enemy. It does do more damage though.

SMN I have found is very hard to use between levels 30-50. It is more of a "let your pet do damage while you cast spells at it from a distance." Most SMN spells also are more based on doing damage over time. However once you get to level 70, SMN does great damage. It is also helpful for solo stuff because you get a tank pet who can keep enemies off you.

Also depending what level you are, you will need to reach level 50 or 60. I forget which one to get SAM. So if you do not have a class at that level, I would choose Arcanist, turn that into SMN until you are able to get SAM. Then you will be able to try out both at about the same level.