Nthing starting with TE3. It's a easy mod that's got pretty much every feature you actually need in a "big name tech mod" these days, smelting, ore processing(also known as "Ore Doubling", or it was occasionally called this before people started adding Ore
Tripling), and a energy system that is somewhat simple generation and somewhat simple storage/transport. It also has item transport and fluid transport.
It's a model of what you should expect from a Tech mod. It, AFAIK, wasn't really at time when TE3 was released(and for 1.6.4 still isn't) meant to be used stand-alone. It's more of a... Example mod for it's power system, Redstone Flux. But it gets the job done and is pretty easy to showcase. A good next step is IC2, if you are okay with some pain. IC2 Experimental is sorta the last legs of IC2. It's a old mod(previously known as Industrial Craft), and it later was updated and became Industrial Craft 2(insert super-script BBCode here). How old? Well... Industrial Craft was released in Alpha. IC2 shortly after the start of Beta. ...How long have we had a "full release" version of Minecraft now? It shows signs of age for sure, but some of it's features are actually still very solid. IC2 crops for example. That's about it, though...
Anyway, once you've gotten use to the pain of IC2 EX, a good next step is to start with RotaryCraft at some point. Fair warning, it's not always easy on computers. RotaryCraft has a in game handbook that details a LOT of things. Kinda covers everything except the calculator you may need and advice on what to make for what. But RotaryCraft is a great mod. Just hope you have enough Iron to use it. A good "how to get a feel for the mod" is at this point getting a Magnetostatic Engine from the base tier to the fully upgraded version. It'll take you through the main sources of power for RoC and give you a decent understanding of how it all works.
For magic mods, well, they usually detail themselves fairly well, actually, but they have very well formed tier systems. Thaumcraft is the base line by which many magic mods judge themselves. A few magic mods exist, and compared to Tech mods, they are far and few between. But the big names these days are Blood Magic(ask @
Padfoote for info if interested, he has a damn good guide on most things in it), Witchery(ask @
SatanicSanta if interested, though seeing how much he works on the wiki, he may just link you to the wiki and call it a day), and for AM2(not in Monster), I know a lot about the power system and the machines, but seek advice on spells elsewhere.