do it in the R22, cheapest and you get the same licence and there are more of them around so more choice in training places but also most likely more R22 at the place you go to, so you won't have to wait ages for a booking during training and later for self fly hire.
Doing it in the R22 will result spending less money compared doing it in a R44 or G2 so you have money left to do an extra typerating.
Also doing it in a R22 or G2 will result in appreciating max power limits, if you train in the R44 you'll never hit the limit which could suprise you on your first flight out with your mates (of course a good school will train for this).
The transition from a R22 to a R44 is very easy.