Reason for switch - more screen real estate.
Tech saavy? - meh, if I set my mind to it I can figure it out but generally just want a bigger platform - that's why I asked about the Note II
One vs S4 - design primarily and reviews show them neck and neck.
So yours is a choice of which Android device to purchase.
My research led me to the same three phones which have been mentioned: the HTC One, the Samsung Galaxy S4 and the Samsung Note 2. None of them are perfect, each has its benefits and its flaws.
I think the One wins the design award. It's a beautiful phone. The aluminum looks much more distinguished than the plastic. That said, I decided against it for several reasons.
First off, I'm not very familiar with Sense, which is the Android overlay that HTC uses. Some users with existing HTC devices are upset by the lack of software updates, but I can't say whether Samsung is any better. In my limited trials at the store, I preferred the Samsung interface.
Second, and it may be just me, but the screen seemed narrower than the S4. I never checked the actual dimensions, but side by side I favored the Samsung. The S4 has the most beautiful display of any phone I've seen.
Third, and most importantly for me, I wanted the ability to replace the battery and use a memory card for extra storage. The One, like the iphone, doesn't offer this option.
Inevitably, I chose the Note II over the S4 for screen size and battery life. All of the tech reviewers I follow on YouTube really love the Note and use it as their "daily driver". That said, it's too big for some people to use comfortably and the screen isn't quite as bright or sharp as the S4.
All three are great phones and I believe you would be happy with any one of them.
Good luck!