Depends on what sub-ohming means to you. For me, 0.3 is about as low as I like to go with an RDA that has high air flow. Magma or origin, more like 0.5.
But both of those setups are sub... 1.0ohm.
If you're not trying to run down to 0.2 or 0.1 or even 0.05, you don't necessarily need to go with a copper mod. Copper takes more maintenance than stainless and even brass.
Since I don't push the outer limits, I like running stainless mods. Aesthetics and less polishing... stainless with a hybrid top cap and no lock rings to forget recessed magnetic button is what I run.
SMPL or surfrider would be my suggestion. Stainless as long as you are not looking to vape a hot, throat hit, super duper cloud setup. Not my thing, but that's some people's nirvana. Copper if you are (XXIX for BCV copper).
All depends on the demands you are going to put on it... some people just like the look of copper too.
I haven't gotten into the vv/vw device's yet, franciscan is very knowledgeable on that one... they are just recently getting to the wattage I would feel comfortable with its capabilities so I am looking into that now (not saying I would run 100+ watts, but I like to stay well below max limits of anything).