I only have experience on the 300, which is a very good trainer. I will have to switch to R44 in the near future (lack of 300s around here at my new home).
From the numbers, the R22 seems a little bit underpowered (and having a smaller safety-envelope). Same (missing power) applies to the Guimbal Cabri - at least in hot & high conditions.
The upcoming R44 cadet (basically a R44 reduced to a two-seater) may become an option in the future, but the IO540 will cost more per hour than the 300s IO360.
Enstrom should be another option.
Maybe you can decide between Enstrom and 300 depending on the nearest available maintenance shop to your planned location?
Thracian