I've never ridden on the Razz but I've owned the Prop for a while and got the Blue Lake this past season. I'm also lousy at surfing but my kids are getting better.
Both boards feel alive and reactive when you are on them. I've ridden on many that just feel dead. The light weight and flat bottom, small fin design of the Phase 5 make it very responsive and fun. My kids (11 and 14) like it better and say it's easier to ride. My wife, who seldom rides, does much better on the IS as she gets the board pointing the right way and feels much more comfortable (stable) when she is on it. For me (200#) the Blue Lake lets me free ride and I'm just too big for the Prop with my wake and skill. Every person I've had try the Blue Lake has been able to get up and ride loose line or free ride on it, if they have wakeboard experience. The Blue Lake has too much floatation for my 11 year old to get up on, and he's a good athlete.
The Razz, I'm sure, is not as responsive as the Prop but that's because it's bigger. Maybe I could free ride on it, i'm not sure.
So Blue Lake is easy to ride and get up on for anyone of reasonable size. It feels comfortable but alive when you're on it and seems reasonably fast, to me.
The Phase 5 design is more squirrelly but very responsive and was easy for my kids to learn on.
Ride them if you can because they really feel different when you are on them.