When you say pre-built coils, do you mean the disposable kind that are used in tanks (like the ones that are used in a TFV8), or do you mean pre-made coils that you put in an RDA? I'm not a huge fan of the tank coils, but I love using pre-made clapton wire. Not the kind you can buy from UD, as that stuff is garbage in my opinion. I get mine from Star Builds - I think the only way to get them right now is through the facebook group, but the coils are the best I've ever used. They offer a variety of different styled claptons (I use the nichrome micro aliens, personally), and will even wrap the coil to fit your specific RDA. I highly recommend them to anyone that uses an RDA.