Rogue or Shadow Priest for Pve/Pvp

Hey im an old wow player mostly played Mists of Pandaria. I'm wondering if i should start on wotlk with a rogue or a shadow priest, I enjoy both classes.
I got some topics i would like you to answer in regards to my problem

(1) Which is the one you think is more needed for icc and if the dps is good (with decent geared).

(2) Which would you think its a best starting class for a fresh player. (im having some trouble about not having recuperate on rogue).

(3) Pvp which one is more useful (im 2.2k xp both on mop so its just a matter of you guys giving your opinion).

(4) Which one is easier to level in your opinion and which spec.

(5) Im gonna buy heroic trinket from Warmane Store for the class you guys help me choose through the above topics, which trinket would you advice me to buy and why for each of the classes.

Thanks in advance for any help.