I really enjoy them both. If you’re only going to get one I would recommend 1914 simply because it plays very differently from the WWII games. Different unit types, different movement and combat rules. If you do, though, you’ll need to go to HBG and get some extra pieces. At a minimum you’ll need more infantry for UK and Germany, and some more chips. Please let us know what you decide!
Edit: One caveat. In terms of what’s in the box, A&A 1914 is an inferior product to 1942.2. The board is split in the worst possible place, all the sculpts except infantry are the same for every power, and the pieces just seem more cheaply made than in other games. And there aren’t enough of them. But I love the rule set and the WWI setting. Just something to consider.