Many people suggest the DW20 pack for beginners because Direwolf20 does a Let's Play series using his pack, which many like to follow along with while building their own worlds. Another nice touch is Direwolf20 provides world downloads every 10 episodes, so you can load his work, take it apart to see how it works, and have a better understanding of how different mods work (and sometimes how they work together).
My personal advice is to make a nice Vanilla base to start, then expand as you learn how different mods work. Even a veteran knows that setting up a Vanilla farm, tree farm, and/or animal pens can reap huge rewards as you get going. From there, find things that annoy you about Vanilla, then find how other people modded the answer in. For instance, I hate Vanilla lumberjacking, so I prioritize a Tinker's Construct Lumber Axe or some kind of auto-farm so I don't have to do it myself. Once you've got rid of the annoying bits, look at the mods you've used to fix your issues, and see what other solutions they provide.
Also, don't be afraid to make full use of JEI (the mod that shows all the blocks and their crafting recipes). I can't tell you how much time I've spent browsing through to see how many ways I can obtain the same materials I need for a project. If you search for an ore, JER (and add-on found in many packs) will tell you what level to mine to find it. It's a wonderful tool, and one I refuse to at without.
