Re safety: in a crash, the safest seat to be in is either the middle one at the back, or directly behind the driver. For anything other than a side impact, directly behind the driver is probably best.
Back seat is always safer than the front, as most impacts involve the front of the car. There's a reason why children can't seat in the front seat in many countries, even if they're in an appropriate child restraint.
And sitting right behind the driver presumably gives you some protection if, on instinct, the driver were to swerve in such a way that they themselves were most likely to be protected from impact. So something's coming towards you head on, driver is going to swerve right and offer the passenger side of the car as the main impact zone.
I suppose, if the driver wants to kidnap you, you're better off in the front because there are probably no child locks there to trap you inside. But overall, given that most taxi drivers aren't trying to kidnap you but do drive like absolute lunatics, I always choose right behind the driver as my seat. Unless I'm with DD, in which case I put her behind the driver and sit next to her (rear seat, passenger side).