Flexilla is a multiwall with composite handle, Nanotek is a singlewall. With those mushballs you are going to want a stiffer bat, in this case probably the Nanotek, even though the Flexilla is going to have a bigger sweetspot. What you really need is an Anderson Techzilla (one-piece balanced multiwall) or Rocketech (two piece ndloaded multiwall).
Anderson Nano's are a little more sought after for singlewall leagues so you're probably going to pay $70-$100
Techzilla's & Rocketech's are going to be in the $50-$80 range. I prefer models built prior to 2008
Not sure about Flexilla's but my guess is still under $100