Have both the Aqua and the Russian. Both provide excellent Flavor and satisfying quantities of Vape. A lot depends on how low you want to go in on your Build ohms. The Aqua is ideal for low sub ohm vaping. Currently have a dual vertical mounted micro coil twisted 28 amg build at .3 ohms. My Russian has a dual series vertical mounted micro with Mundy Magic Twisted Ribbon at 1.3 ohms vaped at 20 watts. Both have extraordinary flavorful vape, of real decent quantity. Both should be in ones rba tank collection, and also the Flash-e-Vapor V2 rba, which is my favorite of all three. Only own one Russian and Aqua, own 3 Flshi's, My first was the Authentic, the second 2 are clones. they vape good at every ohm build I made from .6-1.8 ohms.. Easy to build, fill and maintain. Can re-build without emptying the tank.
There are many fine rba's out there, just have to find the 6 or 8 ones that you really like. One is no better than the other, they all have their own characteristics that I quite enjoy. Wouldn't part with any of them.
Got to start you collection some where, Choose the one you like best for the start or addition to ones collection. If it is your first rba, the flashi and the Kayfun/Russian, would be the better choice. The Aqua is a lot more intense to build and tune in for your desired style, Flashi and Russian much easier to build and vape great from the first build.