There's RPGs and then there's RPGs. If you want something that introduces you to the part of RPGs that is about the mechanics of making a character and developing it, and having a lot of fun smashing monsters, I'd definitely go with Diablo 2. If exploring a beautiful world, seeing cool sights and such sounds more like your thing, Skyrim is probably a better bet. Be aware that Diablo 2 is so old that there's not much of any tutorial, so you might want somebody that knows how it works to help you through the first five minutes.
Honestly, for a starter experience that has it all, and is has a facinating story to follow, I'd definitely recommend picking up something from Bioware - Dragon Age Origins or Mass Effect are both incredibly good games, and both have easier difficulty settings that will make it less of a hassle if you're not an experienced gamer. DA:O is definitely the more RPG-y of them.
Note that all four games I have listed are very different both in feel, gameplay and appeal. They share experience gaining, inventory and quests to do, so they're all classified as RPGs, but that doesn't mean that enjoying or not enjoying one means that you will feel the same about the others.
If you want a more social experience, Guild Wars (2, you mean Guild Wars 2, right?) is probably a good bet for MMOs, but I'm no expert in that area.