If you are talking about atomizers, you should try at least a couple different attys... the Riva is a so called "3.7" pv... which indicates a conventional 3.7 voltage pv ( i would imagine it means the battery, but many include
vaping voltage to the atty/carto ). In reality the voltage is more like 3.2 to 3.4 true voltage.
You will want an atty that is in the low resistance to standard (regular) - 1.5 Ohm to 2.5 (for 510 attys) range. Anything higher than 2.5 is a stretch and the vapor production is minimal.
(although some cartos 2.5 to 2.8 are ok)
The 901 atty comes from LR (1.8 Ohm), to standard 2.8 Ohm... for some reason the reg 901 does work ok on a Riva or eGo type pv. but I like them with a VV higher voltage (3.7 to 4.5v).
IMO the 901 gives a better flavor and slightly cooler vape, and lots of vapor...
BUt most prefer the 510 which is the most popular.
Don't miss the 306 atty too. It's a fun one.