I currently use a four year old Asus UX32VD, with an i7-3517U and a GeForce GT 620M, when I'm mobile. I use it for my daily dose of web browsing and some very(!) light gaming when I'm out of town, and when I'm studying. I rarely bring with me, though, because I don't think it is that much better than my phone for browsing, for it to be worth carrying around.
I do have a desktop PC at home which is my main device, besides my phone.
I think I'll get the i5. The CPU performance and storage capacity of the m3 would be enough for me, but I think I will appreciate the better graphics of the i5.
In a previous post I asked if there are any differences between the thermal management between the three versions, but it seems to have gone unnoticed... Do all three of them use the same heat sinks etc.?