Rhino seems to be an easier choice. Building on Rhino and
moving to Matrix may be an affordable option.
I was discussing Rhino v. Matrix with someone that was trying to
sell me on Matrix a while back and he was telling me that advanced
Matrix training was equivalent to Rhino training. He seemed to be
admitting that if one is serious, one might just wish to learn Rhino
to begin with.
Another possible problem has to do with the fact that the McNeel
Associates which developed Rhino, leased the engine from a third
party and lost that lease at the end of last year. This resulted in
McNeel developing their own engine from scratch. The early versions
of Rhino 3 were heavily included with bugs. They have done an
incredible job of ironing them out in the last year, but Matrix is
built on the back of Rhino, so I would question the resultant
product. I heard that they were very busy buying as many copyies of
Rhino 2 as they could get, buying from retailers or where ever to
keep the quality of their product up as long as they could.