So, as an owner of the HTC One i'l give you a honest thought.
FIRST OF ALL - I don't know how much money you have to spend and I'm not going to get into your life, but if I was in your situation I wouldn't recommend buying the HTC One if you have the S4. It doesn't even matter if the One is a bit smoother and has an aluminium body over the s4's plastic body, at the end of the day they are both top android phones with similar specifications. I moved from the old Galaxy S1 to the HTC One, Now its just amazing how different they are I cant even explain, the HTC One is probably the best phone I've seen out there, but at the end of the day? they are just similar, running the same OS and they both are used the same.
So After giving you my opinion let me tell you this:
1. First, the HTC One is definitely the smoothest android phone I've ever seen - including the Galaxy S4. and By the way the phone runs MC4 and whatever game you pick smoothly.
2. the HTC One has the best screen I've seen, comparing to the Iphone 5, the Galaxy S4 and others - its absolutely beautiful and stunning. Moving from the S1 was a shock to me.
3. The camera is pretty good, it has nice pics though I think I would pick the S4's camera - to me its not a big deal.
4. I know its all about opinions, but the HTC one is just the most beautiful phone ever, People see it and stay with their jaws down. The thing is I might be a bit paranoid, of course after paying alot for it, I cant go commando with it so I've put a protector that should protect it the best, so I cant see how nice it looks.
5. Speakers are just crazy, but seriously, who doesn't use their headphones? and If I've talked about the headphones already I must say that the headphones that come with the One sounds amazing using the phone!!!! I never thought that I could hear so good with the phone/heads.
6. Battery Life - I must say that the battery life is amazing for me!! I'm not a heavy user at all, but my Locations and 3G/wifi are on all day long I use facebook, play some games, whatsapp, Internet, waze and the battery won't end! I usually charge the phone every second day.
So after pointing all these out, the htc one is pretty amazing and its stunning, but If I were in your situation I would keep the money and stay with the S4.
Good Luck,