Depends what you're after, clouds, flavour? What device you looking to use it on and what liquid you typically use? Have you built coils before? Two good genuine Rda I can happily recommend to anyone are the nixon (bottom airflow flavour atty) and edrip t1 (massive airflow cloud maker) both by ehpro which retail for as little as 12quid online. If you're happy with clone then a derringer (flavour) or velocity (jack of all trades lots of airflow options, easy to build). Let us know more and we can give you more options