Hearthpwn

For me it was the original murloc warlock way back when Leeroy was still 4 mana and starving buzzard was a crazy good hunter card. Some people forget that "Murlocks" were just as hated as Secret Paladin and Face Hunter are now. It was easily one of the most frustrating decks to play against. The meta was much different. Zoo Lock was king for the midrange control but if you wanted quick, snappy games you would play an aggressive murloc deck.

Naxxramas killed it for sure. And to be more specific, the Sludge Belcher ended any hopes or dreams of ever taking a murloc warlock to legend again. 

When Nax gave the 1st wing free, it was Midrange Shaman. Jokes on me, since they got crappy cards every expansion after.

Zoolock still one of my favorite decks to play.

Played paladin the most and yet it wasn't a good deck in my arsenal till I crafted tirion

For me it was Mech Mage,I used it to grind the gold for BRM and now I can't stand it anymore.... After playing all that awful aggro I wanted something more interesting to play so I DE all the crappy cards I had,grinded the other dust I needed and crafted Handlock... It's a shame I can't play it anymore.... 

Mech mage, because I played arena only and never touched constructed without a viable deck (reached rank 13 with a basic priest but that was painful enough to stop playing that mode). Only mech mage could be done from the GvG packs solely.

I first crafted Ramp Druid during/after Naxx and did quite well with it for me at the time.

Classic Handlock, havent played much of other decks really, now rock with Demon Handlock

My first ever deck that I made was Mech Hunter on the day of GvG's launch. I got up to rank 9 with it.

Face hunter as far as that was viable otherwise I guess handlock

Oil Rogue, got Preperations in packs. It's a great deck, but but still can't play it for my life lol

 Oil Rogue, got Bloodmage Thalnos in a brawl pack.

mech priest. the first deck that actually got me start winning more games in ranked than i've lost

Midrange Druid and Zoo

Ramp druid (back when The Black Knight was a must), control pally and zoolock

Facehunter and ctrl priest

Mech Mage last January 

Face Paladin - which I I partially designed myself (use blessing of Kings which was nowhere at the time). Was great fun until Leeroy Jenkins was nerfed and ... Sludge Belcher. ;)

Then Zoolock, which is a totally different playstyle. I still think the skill required to play that deck is underrated.

Ramp Druid, got a lucky Cenarius in a pack and loved the class/play-style.

I think it was pre-nerf miracle rogue, at the point everyone and their grandma was playing it. I think I only got a few weeks to play it before the nerf, but it was such a rush finally being able to play a competitive deck.