Expansion Packs ? wich one is first does it matter?

I have a main player a hunter level 47 I am considering the riders of rohan expansion but see the others as well not sure which is the first one to do or if it matters. I have been trying to read up on them to figure it out and I think I am still a feww levls to low for them but am curious to here fro you all and your opinions or recommendations.
thanks