MM
H500 says "few 120s about" - on my field there are more 120s than 500s so it depends where you will fly from.
Your post suggests to me that you have already researched which machines would be available to you, so it is down to the performance that you want rather than availability.
Of the machines you cite, the 120 has the best cabin / comfort (my opinion) but paylod is limited; the 500 has great performance but worst cabin / comfort; the 206 is in between (or is L4 a possibility?). The AS350 has been around for so long that cabin / comfort depends on which model / what fit. Performance is good but flying hr cost is higher.
If you want CPL work then I assume you have looked at the outfits you might fly for, and what machines they have.