TL;DR at bottom

Prior to WoW, I was a carebear; I didn't like pvp, I wasn't good at pvp, and most pvpers were griefing dicks(particularly in D2 camping waypoints)

Post-wow, my first char was an Alliance Warr on Mal'Ganis(PVP)(at the time a VERY horde heavy server, because THE HORDE WERE SA GOONS, which pretty much was a very bad thing. If you know who Goons are I needn't further clarify why it was bad I rolled there cuz the only friend I knew played WoW at the time was there, a raiding gnome warlock. I got to 41ish before I simply got sick of the constant ganking griefing and camping, I couldn't get anything done.

I re-rolled on Shadowsong(PVE). Another Human Warr, sick of being ganked constantly, got this one to 60, tanked, enjoyed it, got a few compliments. However since I didn't raid I just got kinda bored.

So I get Eteocles going on Magtheridon; join DA via referral from another Druid after a very successful 4 druid 1 rogue LBRS stealth run(and this was back in 05 when druids were healbots); raided with them for awhile, enjoyed a little of the GOOD, CLASSIC AV, with Korrak molesting Snowfall's flag and his Winterfall Troll buddies.

When Penny-Arcade & PVPOnline started their little war when the Dark Iron(PVP) server opened, I rolled my Hunter on it, thus starting my first TRUE wow pvp experience...so much mass fighting all the time...it was great. Joined up with the Penny Arcade guilds, even saw Gabe ingame a few times at Redridge & IF at lv18ish and 30ish respectively (just /saluted him rather than play rabid fanboy though ;p); lvl'd it between raids on my druid since Druids were fucking boring back then and the stupid loot rules prevented me from EVER so much as -touching- spelldmg gear(Should've seen the arguments about that on our forums...christ lol); eventually hit 60 with it and pvp'd a fair bit, liked how often I took people out with my trusty boar(BEFORE they were cool! :P), raided a bit too(even had my boar offtank shit in AQ20 before Beast tree was worth shit and I was still heavy Marks lol)

Then, my Ex starts to play...we roll on a new server, Gul'dan(PVP), I figure it's time I made a rogue that gets to a decent level. Dragging her lazy-ass to 60 and farming her epic mount for her(Only the tip of the iceberg; see why she's an ex now? lol) we joined a good active but small guild of rl friends and we(read: I) pvp'd alot, finding stealth to be the best fucking thing ever invented, moreso combined with my Subtlety spec being able to vanish/blind twice. I absolutely destroyed in BGs and I NEVER ever lost to a paladin or another rogue and was quite happy with it; someone ganked us in the world even with her standing around panicking I take out unfair odds and survive even when they don't lol hell of a rush.

In fact, while I was lvl'ing in Desolace around lv34 at the Satyrs near town on my OTHER rogue(Blackwing Lair pvp), there's a lv40 or 41 human pala killing Satyr around my quest area...we fought for about half an hour with neither of us dying and burning our cooldowns + pots repeatedly, he had too much armor and mana regen and I was too damn sneaky/evasive for him to kill, till he eventually fucked up and I finished him off...quite frankly my most proud pvp moment, beating a +6 pala in plate, proving skill can outdo gear. And that, is why PVP = win.

TL;DR: Pretty much between being so freaking bored on my pve 60, and the fun I had in pvp on my hunter and later Rogues, PVP servers are simply less boring. Yes, they're frustrating as fuck sometimes, ESPECIALLY while lvling, but if you want trouble you can go out and find or MAKE it anytime.