You'll want to do both eventually anyway, since you need one at 15 to get to the Job class of the other. Plus, THM gets you Swiftcast - which is the bees knees for casters of any color - and CNJ gets you the ever-handy Protect and Stoneskin.
And if you're just starting out, you really CAN level both! Level THM through the storyline quests (minus the dungeons), and use CNJ to queue for aforementioned dungeons and the basic roulettes you'll unlock. I did something similar with NIN and PLD and was able to get them both to 50 through the course of the Main Story Quest. It might be even easier for you since you'll be sharing gear between the two basically up until 50 as well.
Personally? I like Arcanist for SCH/SMN. Arcanima/Mathemagica/MAFFMAJIK all the way!
And if you're just starting out, you really CAN level both! Level THM through the storyline quests (minus the dungeons), and use CNJ to queue for aforementioned dungeons and the basic roulettes you'll unlock. I did something similar with NIN and PLD and was able to get them both to 50 through the course of the Main Story Quest. It might be even easier for you since you'll be sharing gear between the two basically up until 50 as well.
Personally? I like Arcanist for SCH/SMN. Arcanima/Mathemagica/MAFFMAJIK all the way!
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