Just been in that fab position to have both TC and GB offer over Xmas.
Went with GB, since I have two children and the schedule flying will work better for me.
Lovely people at GB also helped with the vote!
Group exercise after intro to GB, they basically give you a task to do, but its all about how you interact.
Then a semi formal interview for approx 30 mins, nothing technical, but focused on you.
Then you hopefully get invited back for part two in the 737-400 sim at BA at LHR.
I found this okay, but it was East Mids FL60 off 09 to an NDB, track a QDR and then back to the hold for the alt IAP, a go-around to fly the std missed for a procedual ILS to land.
Gentleman who undertake the sim makes you very relaxed and welcome you regardless of experience.
Looking forward to joining very much.
All the best