LGW has recently moved to mostly day trips i.e few nightstops. As a junior bod, day trips i.e. not 2+ day tours can be hard to come by at LHR.
Previously LHR would usually be the best choice for T&Cs. However, BA have managed to work LHR harder within Bidline, the pay scales have been equalised, so it's a closer run thing. If you can come up with some more specifics of what you'd like, I / others might be able to give you a better answer.
NoD