oops..looks like I missed this one..and a belated, but no less warm welcome to the forum!!
Personally I swear by the 55-200mm range for portraits. Certainly 70-300 gives more range, but I rarely find myself in a position where 200mm isn't enough...when combined with my feet.
I don't have hands-on experience with these particular lenses and of course the individual price vs. quality equations have to be weighed in as well in your decision.
Considerations on the require maximum aperture should perhaps be added to your deliberations as well, especially if you shoot indoors or in otherwise dim light. There are primes out there in the 100-120mm range with a larger maximum aperture that would do better in low light. Of course with a prime you might need more room to move though, so it's a trade-off there too.
Good luck with your choice!