hi Melinda, please just ensure you select a one with a removable battery, it is cheaper to replace a battery than the mod, plus you can always have a spare charged up battery so you dont get a vape less few hours.
Will add to that advice, if you choose using pod based systems, ... get pods you can refill yourself. Also, don't buy anything proprietary. Nothing worse than getting chained to Brand X coils, or Brand Z's pods that you have to buy from Company C only. Company C might go out of business the next day, they could gouge prices, not change bad/faulty designs and so on.
I used brand names in my earlier post as reference points. Any squonking box mod would suit me as long as it functioned, caught my eye aesthetically, sold at a frugal enough cost. The same with RDAs. I don't sacrifice on wire though, i like TEMCo wire or a vendor using their wire after cleaning it. TEMCo wire though is usually reasonably clean in my experience. I also dry fire when building a coil on an RDA deck, though. That heats off a lot of impurities.
By the by, just a handy FYI, ... vaping coils when heated can ignite cigarettes. Go figure.