All three frames share the same geometry.

The 721 was their best frame in my opinion because aside from it being lighter and made from 7000-series aluminum (the 725 & 735 are made of 6000-series), it also doesn't have that stupid new seatpost clamp design that is prone to cracking like so:



In true Leader "shooting-myself-in-the-foot" fashion, they stopped making the 721 last year.

If you're looking for something with aero-style tubing and more traditional geometry, don't rule out the Aventon Mataro because of some **** you've previously seen me say on the internet. Their frames have improved a great deal over the past couple of years and are very good for the price.