I play 70 for the nukes.
As a matter of fact, I play any twink bracket for the nukes.
I played 85 pvp for a while, and it was, well, boring. You shot, he swung, you healed, he healed, if you couldn't heal, you're screwed, and as a hunter all you did was run in a circle spamming steady shot and hitting chimera on CD.
I started playing a few months after wrath came out, and didn't get any expansions. So you could say I *twinked* at 60. I truly enjoyed my time at that level....everything was new, I was learning my class (hunter) very well, and felt that I was accomplishing the same, if not more, than the 80s I hung out with. I organized all of the 40 man raids every week, farming them regularly. I soon got all of t1, t2, and t2.5 (AQ40 set) as well as completing the Scepter of the Shifting Sands quest line (or should I say, quest chains of chains of chains of chains) after 2 and a half months. I obtained Rhokh'delar at that time as well. When i had all of these sets, and all of these weapons, and all of these achievements...i was bored. So I bought the expansions and leveled up.
Those next few months were hell. I hated BC, and hated Wrath while leveling up equally. I had been at an artificial max-level for 5 months, and forgot the feeling of having to grind again. I got to 80 soon enough, and joined an alright pve raiding guild, but then, I wasn't so special anymore. My toon was just like everyone else; hustling and bustling around trying to get the same gear, for the same reasons, to do the same things, week after week. Suffice to say, I missed twinking.
Cata hit, and with it, easier leveling. I hit 85 within the nest 2 weeks, and immediately began gearing for heroics, and leveling up my priest and paladin. Got him to 68 before I stopped.
Then, i quit.
For 3 months.
Eventually, I began to miss the view of Kalimdor, and all of it's funny quests, and the task of grinding a level, and the excitement of wow pvp. However, 85 quickly became old again. I continued playing because I had joined a hardcore raiding team, but my heart wasn't in it.
Then, three things happened at the same time. I obtained a Razer Naga mouse, I began a complete overhaul of my UI, including the introduction of several new addons, and my little brother insisted that I join him in a 70 pvp and raiding guild he was in on his shammy. So I leveled up my paladin, and got to work gearing him.
With the completely new UI, and going from clicker to key binder, and having the mouse (which made keybinding feel so natural) my skill level immediately shot up to new heights. it's like taking a level 9 hunter still in their tighty whities from Elwynn Forest, and giving them all blues and BoAs, chanted to 80% haste and 40% crit, and putting it in the hands of an already skilled hunter.
Except this time, I was going to be a paladin. A class I had not played in months.
So I continued to pvp, and adapt to my limitations. Everyone told me frost mages were the most OP class; so I built a frost resist set. Everyone told me rogues would kick my ass everytime I fight one, so I developed a specific strategy for them as well.
So now, I am at a point where I am constantly improving, but I can honestly say I am having the most fun I have ever had. I am already BiS, for pvp, but for each opponent I come across, I have to come up with a new gear set and mentality that will allow me to beat them. Theres no way i could do that at 85, it's too constricting. I love the fact that at 70, you can beat any class as long as you have some ingenuity and understand your class!
In my opinion, I think I play a very underpowered class, with so much room for improvement. I have dueled and fought other prot paladins, and have beaten every one of them, so it's more a game of skill rather than class, and I love that. Instead of performing the same thing over and over, I can mix it up a bit in BG's.
Ok so back to my main point. The nukes. I would sum up my love for 70 twinking as this:
The ability and management of your nukes, coupled with the skill with which you mitigate others nukes, provides a very exhilarating pvp experience that can not be replicated at max level.
Sorry for wall of text lol