Tis a question that is older than time itself, which is better in WoW: PvP or PvE?
There are pros and cons to each but just so you know coming in I am a PvP player.
So this is an odd question because you're comparing two very different play styles that are not always comparable. Raiding is very progression based, clearing boss after boss in a linear progression with your guild. Unless you are a very hardcore guild that does mythic archimonde an hour after WoD was released, then raiding is a very predictable process. The gear is achieved via progression as well, to the point of raiding being a chore. Raiding also has ties to the lore and is a big way for Blizz to continue the story.
Then you look at PvP which is the EXACT opposite. PvP is about going into a que and having to be flexible due to your lack of knowledge of what your team, and the enemy team´s, comp are. Sure, you know you're gonna have a few tanks and a handful of healers, but as to what type, you damage type, how many rogues you have, etc are all a mystery. Personally I really enjoy this aspect, however I have met plenty of people who find it fairly annoying. You also have world PvP that I tend to ignore, simply because it doesn't happen that often or, when it does, itś typically a gank of some sort. You also have Ashran, but no one really likes Ashran so letś just pretend it doesn't exist. You have arenas which provide less team play and more individual skill. If you want the team coordination of a raid but in PvP, challenge a guild and get your buddies together then voila, fun for the whole guild. This all being said PvP does have pretty unfair balancing. Rogues are practically designed for this and any class with stealth will automatically do better than one who does not.
A lot of this comes down to opinion so i´m going to ask, which do you prefer, Raiding or PvP?