I started playing classic Battletech around 1987, when I stumbled across it at a local HobbyTown. I've been playing on and off since, I've always been a huge fan of the universe even more than the game, but my passion for the game was reinvigorated when I discovered Megamek a java-based version of the CBT rules.
Preferred time period: Third/Fourth succession war (pre-Clan)
Love the low-tech, scrounge-for-an-actuator feel of the 3000-3025 period, but also loved reading about the massive RCTs of the 4th Succession war. In terms of game play, I like "level 2" a bit more solely because it's a faster game and time seems always in short supply.
Yep, I'm an Davion, even though I know they're as morally grey as any other house. I love the combined arms flavor of their military, and the Melissa/Hanse wedding was a fantastic story.
I believe I have every source book published (Yep, even the original Star League book) and have relatively easy access to them. I have most of the novels (not some of the Clan-based ones).
MegaMek.net and Mekwars
I started using Megamek when I stumbled upon Megamek.net and have been playing periodically as time allows since 2002 or so.