I'm rotating two married sets of Sony VTC4 and LG HG2 in my RX200S. The HG2 is probably a little better for vape time, but both perform well. I'm a 10W vaper, so I'm not pushing them.
Pick any battery with a 25 to 30A CDR in the green column on Mooch's battery sheet in the post above. Remember that longer vape time is indicated by greater MAH, but CDR is a measure of maximum amperage. The higher the amperage load you put on a battery the lower the vape time. You have to find a battery with the highest MAH coupled with safe CDR at the load you are putting on it.
The RX200S will handle the load and cut off at max current load for protection. As other posters said, stay away from Efest for high amp vaping. Stick with Sony, LG, and AW for quality.
Here's a good explanation of how multiple battery mods handle the current load and voltage requirements of sub ohm vaping. Remember, the batteries in your RX200S are in series, so 3 x the nominal 3.7v = 11.1V and the current handling capacity of your mod jumps to 3 x the amp rating of the battery you use in a triple configuration.
PSA: You Don't Calculate Current Draw on Regulated Mods Like You Do on Mech Mods • /r/electronic_cigarette
Here's Mooch's explanation of how multiple battery mods handle the load. He uses the RX200S as one of his examples.
Calculating battery current for a regulated mod • /r/electronic_cigarette
Mooch's blog | E-Cigarette Forum
Just pick the batteries with good current and MAH ratings. As amp ratings rise, MAH goes down and vice-versa.