It depends on what you're looking for. First and foremost is finding two compatible ladies. Nothing sucks more than having blue balls because the two girls are awkward around each other and you get a glorified four hands massage. Then, you need to determine if you want both girls there during the finish or whether that's not important. This will determine if your session is a duo or a fling.
Personally, I find the Flirt Flings are the best bang for your buck. It also alleviates any awkwardness two girls may have with each other don't work out because you'll always have each of them alone for 15 minutes. Not to mention, you get a 45 minute session for a lower price than a 30 minute. That being said, having two girls work you to sensory overload is a heavenly experience if you get the right pair.