Hi
I don't think any base is particularly over crewed even though LGW is a bit of an odd one. There, more pilots are needed during the winter months than during the summer ones. Hence it tends to be a "fat" base.
As for bases on joining the airline, MAN seem to be the trend yet this means nothing as guys who had initially asked for LGW were told MAN, only to end up at LGW by the end of the ground school.
The less likely one are probably BRS as it is small but popular.
Anyway, all done by seniority so for example my 1st choice was LGW. I got LTN and 6 months later was given LGW.
Guys who joined after I did probably required less time than that to get their 1st choice if any time at all.
2 bid round every year so the situation is rather fluid.
WRT Long Haul. Not that much up sto speed with it but MAN, LGW main bases for the summer so the pilots based there will probably do it.
During the winter it is different because it becomes what is cunningly called "Winter Long Haul Pilots list".
Basically all bases can do it, as long as you are a long haul pilot which once again is established according to your seniority.
Time to get on the list varies with the Long haul programme, retirements ect... I am not far and I have been here for about 15 months. Some guys from MAN would have been on the list for quite a while already though.