Discounting rebuildables (RDA's RTA's RBA's and the like) which I feel are a different kettle of fish, I rate evod/protank/davide style bcc's as the most consistent and reliable 'off the shelf' tankomiserthingummyjigs. A quick 'however' about the protank II is that imo, the quality of the coils that come with the kit, have, for reasons best known to the manufacturers, deteriorated in terms of quality to the point that they can only be described as 'pants'!
A strange scenario, seeing as the 'packs of five' replacement heads are all fine (if you buy new heads instead of rebuilding your own). Something to be considered, with all tank systems, is that your battery has to have enough oomph to power the coil and vapourise the juice. The poor old tank seems to get all the blame for leaks,gurgles,floods etc, which is very unfair when all they are asking for is enough power to vapourise the juice that the vaper is sucking onto their coils.