Guild Wars 2

For Dungeons/Fractals and WvW? :>

I’d probably play a phantasm Mes and a staff Ele respectively

Thank you!

It is not a big difference and it depends on a lot on how you play and what you prefer.
In dungeons both do well, though bezerker mesmers are more welcome in e.g. speedruns in CoF, though ele’s are better for general usage. On top of that mesmers are more pushed into specific builds (portal/feedback/timewarp).

As for WvW the tables are turned. Mesmers are slightly OP in 1v1 battles and can be used mroe for general purposes. While the ele is more effective inside a huge zerg (just AoE them all.

So it comes truly to playstyle and personal preferences imo.