I had clockwork gnome originally, he's good if you can fit him. I went against a rogue that had the dream opening: coin + mech warper + clockwork gnome + clockwork gnome on turn 1.
That's hardly a dream opening. Nearly going into top deck mode on turn 1 just to get an easily removed board isn't going to crush matches the way undertaker dream openings could. While you'll get some face damage in, with almost no other cards in hand, it's entirely too easy for your opponent to stabilize in only a couple turns.
For a mech rogue, I can think of a few better "dreams." Turn 1 double cogmaster into a mechwarper. For many matches a turn 1 coin hero power into turn 2 auto barber as long as they don't play a 3 health minion. Otherwise Turn 1 coin mechwarper. Turn 2 mechwarper for 1, 3 drop for 1 (sensei, tank, or harvest). And what I would consider the best one: Turn 1 cogmaster, turn 2 double mechwarper, turn 3 whatever else nasty (dagger/deadly poison, free 2 drops, 1 mana 3 drops except tinkertown).
Clockwork gnomes are just questionable, even for free. To me, they're only good for undertaker lists, otherwise you're better off with cogmasters if it's a tempo mech deck.
And that's my problem with most mech lists. The only turn 1 "power play" is the one listed above, uses only neutral minions, requires going second, requires the 3 card start, and just isn't very good on top of all that. Now of course mechs aren't trying to be the new undertakers as they're more about the turn 2-4 curving out but those are still extremely dependent on mechwarper to not get mana clogged. It's a solid if underwhelming mid-game tribe and I think only 1 or 2 mech decks will land in the meta (probably mage and rogue). My rankings so far:
1) Mage. The most obvious but doesn't seem quite as rounded as the tempo/control hybrid mage that is good against all comers. Gain some synergy and mid-game board presence at the expense of reactionary plays, removal, and a strong late game. The chugger is quite the 2 drop mech for early game and the blastmage is really good. However, I think the best thing about mech mage is the hero power. If you're brawling for board control, the ping adds a lot of reach for trades. Also the obvious finisher with Antonidas and spare parts to fill up on fireballs for the finish. Antonidas has now reached broken levels of potential with spare parts being able to easily draw 2-3 fireballs the turn he comes out.
2) Rogue. Some kind of mech aggro deck should be good after some meta tuning. A mech start in the first few rounds into a sharpsword oil finish can be really strong. Barbers are great in any rogue deck and sensei has a lot of potential but is just sort of slow. He is a huge target for removal which is nice as he also creates a big threat on board that isn't himself as well. And if he gets more than 1 pump off you probably won the game. Fel reavers are strong here.
3) Priest. Mech priest probably vies at the top for anti-aggro decks (competing with its own higher aggro potential deathrattle priest). Many of the new mechs and synergies go well with healing, even all the 2/3's. I'm mixed about other mech matchups though. In a mech priest vs mech mage, I'd rather be playing the mage. "Beatings available."
4) Warlock. Not much class specific mech synergy (fel cannons are risky, even with near full mech lists) but zoo gonna zoo. It's always been about card advantage and maximizing synergy in the 2-4 drop range. It's solid but seems better on paper. They still need to draw into the start like anyone else as zoo can't afford to be tapping turns 2-3.
5) Shaman. Shaman has huge burst aggro potential with the windfury mechs, flametongue totems, rockbiter weapons, and spirit wolves to keep them behind taunt walls. Throw in some fel reaver finishers and things can get out of hand quickly. They're just really fragile and easily shut down.
6) Warrior. Warrior mid-range has always been just short of viable. A lot of good synergies already exist with warrior mid-game and they got a lot of mech cards. Warsong commander, anyone?
HM) Druid. They got 2 new mechs but no mech synergy. Wild growth seems too slow but innervates could combo out some crazy early boards with mechwarpers although losing another drop early on for the swing leaves you without cards in hand. Maybe a mech start with the double force/roar combo to finish? Haven't seen anyone try it and haven't tried it myself.
Garbage) Paladin/Hunter.
And why I don't like those lists:
1) Mage. Tempo/control mage is better although not by much.
2) Rogue. May be the best rogue deck now since they don't have a lot of strong archetypes with miracle getting shit on. I don't know if straight aggro would be better.
2) Priest. Control priest is better.
4) Warlock. Regular ass zoo is better, demons are better, and probably demon/zoo hybrid as well.
5) Shaman. Their mech list feels like old murlocs. Feast or famine. That's not a good thing.
6) Warrior. Control warrior is better. No hero power synergy with mechs at all and their removal outside of weapons can get clunky.
HM) Druid. Would still require a force/roar finisher. Druid has been severely raped by the dominating Antique Healbot. Even non-mech druid lists struggle to find lethal in the new meta with it. Shows potential but seems bad.
Garbage) Paladin/Hunter. Go play a different deck.