S-Pen is a huge difference. I really like the HTC One, but i have no confidence they will be around much longer. While updates are not the end of the world, if a security exploit occurs, I want my phone manufacture to fix it, not sure that will be the case with HTC. The G2 has a beautiful screen, but the skin turned me off. Neither has the S-Pen, which I use all the time on my Note 2 and now on my Note 3. BTW the G2 and the rumored Nexus 5 along with the Note 3 were on my short list, but after 5 minutes in the store, it was a no brainer, I had to have another Note.
If you don't use the S-Pen, then save some money and get the G2 (if you like the skin).