I know going from the UK to the US I have had packages shipped by " Parcel Force " and DHL would deliver them here (US). They always did a great job and were fast (3 to 5 days) but DHL is going bye-bye here in the US now. I would think UPS or USPS would be fine, go with the cheapest since its so costly.
Also to the UK'ers...what is Parcel Force ? Is that like your goverment post office (USPS here in US) or like UPS/FEDEX (private carrier) ? I always wondered and never asked :)