The thing is, if he goes with the one that never goes to instances, he's gonna have a tough time enjoying it. My friend has a 70 priest that isn't keyed yet, in a guild where everyone else is keyed. They don't help him out, so even though he loves his priest, he can't enjoy the instances with his guild.
If you're looking for solo power, a paladin is another good choice. It isn't a pet class, but I'd like to see a lock or a hunter handle 9 yellow mobs or 4 yellow elites (in solo) without blowing more than a 5min CD. And ofc a paladin is going to bring a lot to the group. Then again, if you used to have a druid, maybe a hybrid isn't for you...
Between a lock and a hunter, I'd say it isn't a question of who's wanted more, but of who's hated less. Hunters are known for ninaing loot (mainly b/c there's so many hunters chances are you'll come across more ninjas), causing wipes with pets, and for having horrible CC. In fact, my hunter never needs unless that item is an upgrade for me, I am able to PREVENT wipes with proper pet management if the tank dies, and being a survival hunter I can out-CC a mage.
Locks, on the other hand, don't do much damage on trash, and are known for fearing inside of instances. But, they both have their advantages - both have good long-term DPS, locks have soulstone (while hunters can FD and use cables if their engineers, not as good but close), locks have a bigger variety of pets, hunters I think have a better pet (lock pets are better at their specialization), hunters can kite, locks get underwater breathing...its really up to you. The main question I guess is, would you rather switch between 4 demons, or just keep 1-2 general-purpose beasts?
Also, at skulldiver, the problem with levelling a lock to 20 is it's one of those classes that keeps building up it's potential (like a druid). Most classes, i.e. rogue, hunter, etc. you will play with a similar style - just more abilities - from 10 to 70. But druids and locks, who keep getting more forms and pets, will change your playstyle and options.