She swings both ways. Arcanist or 10T. She can also hire 3 different Bayou models (Sparks, Survivors and Mechanised Porkchop).
I don't know much about the 10T but people say she's got better options in Arcanist. I'd agree as Mecharachnid, Soulstone Miner and Steam Arachnids all go great with Mei. Joss, mobile toolkit, Kandara and firestarter have some synergy/speed to keep up.