Nunu and vlad are pretty shitty right now.
Regardless, you're limited to starter champions for the first 7 levels.
Really? What was nerfed about them?
Wouldn't call Vladimir straight-up bad, but given the number of problems that he has I'd far from call him a safe pick. His early game is weak, when top lane as of late tends to favor immediate aggression. He does scale relatively nicely late game, but his team comp needs to compensate for him somewhat since he won't be the designated "beefy initiating brawler" most have come to expect for a top laner. He can splitpush, but he's nowhere near as proficient at whittling down towers as melees who buy Hydra (for instance).
Nunu on the other hand has no redeeming qualities anymore with how badly everything in his kit has been nerfed. Can't counter-jungle well because of the Season 4 changes not favoring this style anymore in conjunction with Consume being thoroughly subpar now. Loads of bad match-ups as a support nowadays; even back in his heyday he wasn't that strong for that role, because his primary purpose was "Blood Boil the everliving hell out of my ADC" whenever that skill was off cooldown and zoning with Absolute Zero (now ignorable with all the mobility). He used to be effective in top lane, but everything that made him a force there has either been gutted or removed (never mind how League changed since then).
I'm surprised he hasn't been due for a rework yet with how Riot dislikes him; instead they waste their time on Trundle, Skarner and Xerath.
You realize that Nunu got picked and subsequently banned in pro play today right?
Oh yeah, what an incredible pick and ban Nunu was for OMG and TPA respectively. During OMG's match all he really did was 'secure' a dragon after fnatic politely moved away from it, after having Baron stolen from under his nose. Nunu, unable to slay Baron with Smite + Consume. Incredible feat right there. TPA on the other hand got their shit pushed in regardless because (among other misplays) they were stupid enough to remove worst Season 4 champion™ from OMG's roster after said champion had a laughable performance, instead of banning a champion that's genuinely threatening. Amazing strategic call.
Pro players / teams are far from good enough to
not make stupid decisions before individual mechanics even come into play, and I've seen plenty of that yesterday with or without Nunu enjoying competitive relevance. His brief appearance during the All-Stars tournament doesn't change the fact he's pitifully underwhelming; every dog has its day.
Top Nunu is definitely in troll/cheese tier, a bit like Leona. You can't be killed and can't kill them without a gank, but in the process, you ruin their lane and still bring a a tank and utility to your team.
I used to main him and top Nunu is garbage now. Level 2 cheese by killing golems is gone, his sustain has taken a big hit (unnecessarily so), his snowball isn't that potent anymore and top laners are now resorting to playstyles that he was originally weak against all along (hard-pushing the lane). Him fulfilling the tank role is an overstatement, but I suppose he still has some utility by being a "solo Baron at 15 minutes and use Blood Boil on auto-attackers" champion with the right build.
If you want to be a pain-in-the-ass for top lane melees with loads of late game utility, just pick Karma instead.