The FC cabin has the mood lighting which I really like, which the Thomsonfly aircraft do not have.
The meal tray is in your arm rest you actually get more width in the Thomsonfly premium cabin seats. The seats themselves are comfier on the first choice aircraft as they have more padding in the seat.
The former first choice aircraft however are showing their age and some need some TLC where as the Thomsonfly aircraft are better in that department thanks the the darker more sturdy leather used.
After reading feedback from customers who have travelled in both types some prefer the smaller more individual service on the ex Thomsonfly cabin as it allows the crew more time to give you attention.
The way they cabin is layed out, you also get chance to disembark first on the ex First Choice Aircraft where as its a bit mixed on the Thomsonfly ones, depending where the airport brings the steps/airbridge too.
The IFE tends to be less problematic on the Thomsonfly 767's because they have less to break and go wrong being touch screen(no remote for someone to damage)
They both have their pro's and cons it depends what your looking for.