My two favorite RDAs are Origen and Magma fasttech clones. Of course my IGOs, Nimbus, Patriot are still excellent RDAs.
Number one for me is Origen - decent well + small lip, love the look (brushed and shiny stainless), sufficient airflow and doesn't leak, top cap easy on off, shorter than Magma. Fits flush and looks great on my Hana MODZ mini V3 - nice small setup.
Magma as mentioned by others: super wells (but no lip), I like the screw top, super airflow adjustability, easy build platform, but always remember to carry a tissue for leaks out of air holes (from condensation + non-evaporated spits of juice from coil).
Oh almost forgot the Magma 510 screw is long - doesn't fit flush on any of my decides (MVP 2, Hana, SVD, itaste134). It is unfortunate that there is not a standard 510 male connector length for toppers.
Both are keepers for me and used regularly.