Core families
You have F1 (CC3D), F3 and F4 (Rev) hardware on the market. F3 is newer and fills the gap between F1 and F4. F3 has the core of F4 but running at lower clock, also a bit less RAM but more than F1. Also F3 has hardware inverter for serial port which can be handy for FrSky telemetry. There are several F3 boards supported by LP in next, but no GUI for all of them yet.
What is more important clock or ram ?
You shouldn't care about CPU cycles too much, people will always need more and more CPU to calculate faster, without flight benefit. What you care mostly is RAM I think which allows more features to run.
With Revo you can for example use Autotune module, which automatically attempts to tune your PIDs. You have to validate them yourself of course, it's not a good idea just to run it and fly it. Some pilots experience this module to give over-estimated yaw PIDs and have to tune their PIDs using other methods (i.e EasyTune or more time consuming Ziegler-Nichols method).