~ All of the grass starters seem decidedly 'meh' in terms of battling capabilities.
Venusaur is OK I guess; in OU he's got a few viable options, in the form of seeding, Specs, and a decent sleep move. Most importantly, IMO, he can absorb Toxic Spikes on impact. However, he's got issues in that his two STAB's, type wise, are offensively very 'meh', though Leaf Storm goes
some way to make up for that.
Meganium, being top-tier in UU, has quite a lot of decent support options, most notably seeding, the screens and Aromatherapy, but is let down by a very poor offensive movepool that is limited to STAB and Hidden Power. IMO, the worst out of all the grass starters, and certainly one of the least OU-viable starters in the game. He looks so unbelievably bland too >.<
Sceptile, being the fastest Sub-seeder in the game, has some kind of use in OU. Viable Specs (LEAF STORM :) )and Swords Dance sets too add to the threat this thing can pose. However, apart from sub-seeding, it, as do most other Grass types, struggles with movepool issues. Whilst lots of things have helped Sceptile this gen, the addition of Roserade is decidedly reminiscient of what happened to Flygon as a result of the addition of Garchomp.
Torterra's typing and stats leaves it pretty unique, with two decent, high powered STAB moves coming off a decent attack stat. The massive weakness to arguably the most common offensive type in the game is unsettling, as is the lack of a water resist, which we've come to take for granted from most Grass types. Much less limited than the others in terms of movepool, and actually has enough offensive options to fill a decent Choice set, which isn't something any other of the grass starters can claim (Specstile might argue, but it's got to rely on Focus Blast, which doesn't compare to Torterra's offensive movepool)
~ The four Fire starters are all very decent; all are generally, in themselves, OU viable.
Charizard suffers massively from the Stealth Rock weakness, but is still an incredible threat with Belly Drum. Viable Specs sets are a possibility, but due to that horrible SR weakness Charizard isn't really quite as suitable for the hit-and-run play style that Choice items involve when compared with the other various Fire types.
Typhlosion's got a massive boost this gen thanks to Eruption and Choice Scarf; however, he's incredibly predictable, and lacks a decent special movepool besides STAB and Hidden Power (Well, Focus Blast, but w/e.) Stil capable of putting dents in pretty much anything though.
Blaziken: lol Infernape. It's only really got Baton Pass, Reversal and Agility over the monkey; he's decidedly average at BPing, and Reversal won't work without extortionate support due to SS. He's still a very good Pokemon, it's just that Infernape is better than him in almost every way.
Infernape: Fantastic movepool, great stat distribution, lack of an SR weak makes this, without a doubt, the most competitively viable Fire starter. Wildly unpredictable.
~ As for the water starters, their competitive viability seems to be very varying.
Blastoise, a decent bulky water/spinner in UU, struggles to compete in OU due to poor offenses and a lack of a reliable recovery move. Sure, it's got other uses and sets, but they all scream 'GIMMICK' at best, with the possible exception of the ReSTalk set. Probably ties with Meganium as 'worst starter for use in OU play', it's just outclassed.
Feraligatr will always have to live in the shadow of Gyarados, though the lack of an SR/quite so big Electric weak are points in his favour, as are Swords Dance, Focus Punch, Torrent and Crunch. However, he lacks the resists, Taunt, Intimidate, and the raw attack that makes Gyarados so scary. He looks awesome though.
Swampert is undoubtedly the best of the water starters; the ability to take on most Electrics with ease is something other bulky waters would kill for. The Rock resist is invaluable, as is the Sandstorm immunity. No reliable recovery hurts it.
Empoleon has the surprise factor on it's side; being able to tank with it's unique collection of resists and decent defensive stats, or it can sweep with Agility/Petaya/Torrent. Again, would be much better with some form of recovery other than Rest.
