For me the main question is "what do you want to do with it?"
Is it for you to fly (with family / friends) then whichever you would rather be in. A bit like a car. It seems that both will do the job, so which is closer to your requirements?
Are you significantly obese? Sounds a little personal but if you and your better half weigh in at 120kg each then CoG is going to be a problem in the EC120 once you load the back with friends / overweight children.
If you want a workhorse for shifting loads (internal / external) then for me the R66 has it. Cheaper purchase cost and good payload. I would not choose a new EC120 as a pack-horse (but a 12-year inspected machine at under £500k, now then.......). I would rather go for an older H500, Jetranger
If you want to make some money back by leasing it to a club / school for SFH then perhaps the R66 might just shade it - easier transition from the R22 / R44. However, does the R66 record any abuse like the EC120 (Asking here, I don't know). If not then the EC120 is definately the way I would go because I have heard too many stories of expensive bills for over-torque / over-speed events that no-one admits to. The EC120 tells you which flight the event occurred on so that you can nail the cost to the offender.
If you want to make money by leasing it back to an AOC for passenger transport work then the EC120 has it - much easier to get charter bookings for Ascot in something the general public thinks is a "real helicopter".
Neither one is "better" than the other, they offer different things.
Buy one.
Fly it.
Come on PPRUNE and tell everyone else they bought the wrong machine. (That's what we all do; it's a true participation sport and, at times, a team event.
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