Sienna's definitely petite in both height and build, while Izzy is actually quite tall but is very slender. Both have accurate pictures on their websites and both advertise here.
I've seen both ladies (not for Greek, not my thing) and both are great for different reasons. Sienna is a mature provider with enhanced breasts and a body that would be impressive on a 20-something woman. If you like dirty talking and more of a PSE performance from a MILF, you'll like her for sure.
Izzy on the other hand is younger and more of an intense GFE experience with all the PSE moves you can think of. I'm definitely biased as I feel we have great chemistry, but others have also noted she seems to really love her work and is usually as into a session as you are.
Damn - now I kind of want to see both ladies again. Stupid bank account... ;-)