Different mech mods do hit differently. You'll find the material that the contact pins and the mod itself make a huge difference. Stainless steel is the most durable, but has the least conductivity, and therefore hits not as hard. Next comes brass, which is a happy medium between durability and conductivity. You'll find a lot of stainless steel tubes using brass contacts. Copper is one of the best conductors, but is a softer metal that oxidizes quickly. Finally, silver is the best conductor, but very expensive, so you'll usually only see silver plating, not pure silver itself.
Other factors play, as well. The positive contact is usually a pin or a direct connect to the 510 connection through a hybrid mod. The negative contact is actually the tube itself, when the button is pressed, completing the circuit. As a result, springs for floating pins reduce conductivity, since it takes the current up a narrow winding channel. One piece designs normally hit harder than sectional mods, that have different sections for different battery lengths. This again goes back to less obstacles for the current to pass through.
Most clones from the well known clone makers hit just as hard as the authentic's. This includes companies like EhPro, Hcigar, Infinite, Cigreen, and a slew of others. You can usually find a review of the clone you're looking at. Fasttech has those companies' products, as well as unknown brands. But the reviews are usually there, if you search "xyz fasttech clone."
For batteries, it depends on what you're doing. If you vape regular resistance only, like 1.0 ohm or more, you can use most IMR 18350's, 18490/500's, and 18650's. If you vape or plan to vape sub-ohm, stick to 30 amp 18650 IMR batteries, like Sony VTC3/4/5 or purple Efest batteries. Personally, I do sub-ohm and only trust Sony VTC's because of their proven track record.