I'm heavily considering getting the EVO, mostly because my nearly two year old 3G is starting to show some signs of diminished battery life. No matter what, I am getting a new phone in the next two months.
1) I have massive hands, so I don't think the phone size will bother me.
2) The HTC Sense UI is REALLY slick. This and the Incredible are the only two Android phones that have made me consider leaving Apple. If you haven't seen the UI yet, I suggest checking it out. Apple could learn a thing or two. the iPhone UI was amazing three years ago, but it is really showing its age.
3) The Sprint plan would save me ~240 a year on my phone bill.
4) Android has a number of really nice features that would sway me over. Not multitasking, I could care less about that, but the built-in GPS navigation, voice to text, and A2DP support.
5) Replaceable battery. Having a fully charged 2nd battery to run to would keep me going on even the busiest days.
If I was in a 4G city, it would be a no-brainer, but unfortunately, I am not one of the lucky few.
What it comes down to for me, is to see what Apple's iPhone announcement looks like. We have an idea about most of the hardware now, but we don't know battery life, or if there will be any other additions to the 4.0 OS that will only work on the iPhone HD (or whatever it is called). If the new iPhone uses a slightly better radio, we might be able to get faster download speeds than the 3GS, which would be a nice improvement too.
So, I'm not going to be in line on June 4th to pick the EVO up, but if the new iPhone presentation doesn't blow me out of the water, I may be there June 7th.