IMHO DAO, it's the less aged of the two. To play Arcanum requires a certain mindset. It's janky, even modded, though with the fan patch it works very well. The GoG version is superior to Steam, as always, so you might not even need to mod it though I still advice you do. I love Arcanum, but I have only ever finished it once (last year actually) despite trying more than 5 times. It's a fantastic game at its core, but it's so different from games made today it takes more effort to play it if you don't have the nostalgia helping you. DAO is good straight from the box. Sure, it's old now but it works. The controls, although perhaps janky (I always struggle a bit with the camera when I reinstall it, heh), is still easier than Arcanum.
I'd say comparing the two is like choosing between Fallout 2 or Mass Effect 1. They aren't similar, they play differently, they will have very, very different experiences for you. Both are great in theiw own ways and shouldn't be compared, but based on your post I think you'll have a harder time getting into Arcanum than DAO hence why I recommend the latter over the former.
