Would anyone be able to give me a brief idea of the xp/h at different Dungeoneering levels? I'm currently 19 I don't know where to start! Also... is it slower to train than Slayer?

the highest can go to around 50k+ per hour when you are at f35, 5:5, and other bonuses

faster than slayer imo

Sadly there is too many X factors in dungeoneering so really it all depends on your team and how it is they do floors. Also depends on what kind of floor you gets doors ect. I have done two large floors in 1 hour for about 45-50k each. A pro team can easily get 80k an hour but at lvl 19 i suggest you just hang out and just observe and piece it together for yourself its kind of hard to explain you will have to see for yourself just go to w117 and get teams there.