Pidove - Low Tier
Availability - Very early (Route 20)
Notable Moves - Fly, U-Turn, Roost, Return, Taunt
Stats - Decent attack and speed, average physical defence. Rest is bad.
- Description -
Fifth gen's early game normal/flying pokemon. Arguably the worst so far. It lacks super-effective (and even neutral) coverage, which is bad for something designed to be a fast attacker without boosting moves. It's not as bad as Purrloin/Watchog etc. and it has SOME use early game, hence Low tier instead of Bottom. But it's just outclassed by so many things.
+ Caught very early
+ Can do some work against Roxie's Venipede and Burgh's pokemon
- Horrible special attack, has only special flying moves until you get the HM for Fly. Return will be your best STAB, and alone it doesn't do good at all
- U-Turn requires some "grinding" at the PWT, so you'll be stuck with only two attacking types (Normal, Flying) with common resistances (Rock, Steel)
- "Just get a Braviary" (or, if you don't need the Normal/Flying combo, just get any other flyer. It will mostly do better)
Sunkern - Bottom
Availability - Very early (Route 20)
Notable Moves - Leech Seed, Sunny Day, Solarbeam, Giga Drain, Sludge Bomb (Need to use Tutors or keep it unevolved until lv41), Earth Power (Needs tutor)
Stats Bad. Sunkern actually has the WORST base stats of any pokemon, ever. Sunflora has bad attack, OK special attack and 75-75-85 defenses, with a Speed so horrible not even Chlorophyl will help.
- Description -
Your worst option for a Grass type. With Sewaddle it's the only Grass type you can catch for a little while, but it doesn't mean you're gonna need it. Can't do anything against Roxie anyway. Pain in the butt to level up until it's evolved, and even then, it will fail dealing with the endgame (though it helps against the final Gym, so does any other grass type).
+ Nothing. It's that bad.
- Caught very early in the game. Yes, it's a con, as you will have to spend MORE time with its base form before gaining access to a Sun Stone.
- Very generic grass type movepool, doesn't even get Giga Drain by itself unless you keep it as a Sunkern until level 41 (Good luck). Can't abuse Leech Seed because it's just so slow and not exactly bulky.
-Only viable strategy is with Sunny Day and some attacking moves (you only have three options in Solarbeam, Earth Power and Sludge Bomb), but you're so slow that doubling your speed won't do any good. Not even ingame. Unless you need to outspeed Gigalith.
Psyduck - Middle Tier
Availability - Very early (Floccesy Ranch)
Notable Moves - Surf, Hydro Pump, Psychic, Ice Beam, Brick Break
Stats Good Special Attack and Speed, usable Physical Attack, mediocre bulk
- Description -
Special counterpart of Azumarill. It's outclassed by many water types (most notably Starmie) but you can get it so early it can really help out. Not as good as Huge Power Azumarill but it's a lot faster nonetheless.
+ Available very early in the game
+ Quickly gains decent special attacks (Water gun, Confusion, then Water Pulse)
+ Even the weakest psyduck will at least 2hko Roxie's Koffing with Confusion and do a nice chunk of damage to Whirlipede as well
+ Water Pulse looks so cool
+ Water is a really good type you often don't have access to early game, if you don't like Azumarill this works great
+ once taught Ice Beam, it's fast enough to decimate most of the Champion's pokemon (barring Lapras) with super effective attacks
- Not extremely useful against most major battles
- Average to subpar on the endgame, don't expect many OHKOes with just your neutral STAB
- You'll probably catch it as a temporary poke to be replaced lategame when the really good Waters are available
- poor coverage midgame unless Blizzard is used (not very accurate)
Mareep - Middle-Low Tier
Availability - Very early (Floccesy Ranch)
Notable Moves - Discharge, Thunder Wave, Power Gem, Signal Beam, Volt Switch, Thunderbolt, Light Screen
Stats Poor physical attack, good special attack, good special bulk, decent physical bulk, bad speed (not as horrible as Sunflora though)
- Description -
The earliest Electric pokemon you can catch, it's a decent tank that can dish out some damage, spread paralisys and maybe setup Light Screen
+ Caught very early
+ Learns Thunder Wave immediately. Great move for the early game
+ Decent coverage through only Level Up moves (no shards wasted)
- Works pretty much against every Gym leader and early game major battles, except for Elesa, Clay and Drayden (Though Thunder Wave on his Haxorus will make your life a lot easier, and ampharos is not WEAK to the gym, it just can't use its STAB).
+ Tanking a hit and Volt Switching is a very reliable way of sending your fast-but-frail sweeper into battle
+ Who wouldn't give it a hug? Except you'd get electrocuted. Yeah, Static is a decent ability for a change, since Ampharos can actually take some hits.
- Outclassed by Magnezone as a wall, and Eviolite Electabuzz is probably bulkier and faster, then it turns into Electivire which has superior coverage, speed and offensive stats. It's a good poke, but basically ANY electric pokemon does his job better.
- Barring the final Gym, it hardly has any use late-game. It's slow like Magnezone, but lacks the awesome typing to take hits. Thunder Wave helps but not really, you end up taking hits from pretty much anyone.
- Coverage moves are great midgame, but they end up lacking raw power. Don't expect to oneshot anything not weak to your Electric STAB.
Hope it helped with the early game choices