Can't recommend you anything as I don't use mech mod. But let me tell you a few points so that you can decide on your own.
1. What is the material of the mech mod?
Different material have different electrical conductivity. The different conductivity of metal are stated in the graph above. The better the conductivity, the lower the voltage drop and the harder the mod will hit. Some mod have full copper internal but the exterior is made of different material. In that case, look at the internal material.
Anyway, stainless steel is basically just iron with some carbon. And brass is just copper with some zinc.
What is voltage drop? Well in the most simplest term:
All electrical component in a circuit will contribute to the overall resistance, no matter how minor it is. This includes the coil where you want most of the resistance to be. But at some point of the mod (tube junction between top cap and bottom cap, battery contacts and 510 connection) there will be minor resistance. So that mean not all of the battery power will go to the coil. It will be wasted as heat along some point. That's why sometimes your switch will get hot (high resistance at switch) and why experienced vaper are using hybrid 510 connector to get direct connection to battery.
2. What is the 510 connection of the mod.
Is it a normal 510 or is it a hybrid 510? As said before, hybrid has direct connection to battery, so it will have less voltage drop but at the same time hybrid
are only compatible with some atomiser. Not all atomiser will fit hybrid and the using ill fitting atomiser will result in shorting the battery.
3. Does it have a locking switch? Is the switch recessed into the mod
All these are basic safety mechanism to prevent firing of mod when you don't need it. Do you want the hassle of locking the switch or do you want the convenience (but a little less safe) recessed switch?
4. What size of battery do you want to run?
Some common sizes are the 18350, 18650 and 26650. There are more battery sizes though.
Will update more if I have any more ideas haha. But I'm not sure about the quality. Just watch some review video on the mod you want and decide.