Should I upgrade to IPS or 120Hz?

Hello,
I'm currently using an Asus VH236H (60hz TN display) and I'm quite happy with it. I purchased this monitor because I used to game on my console quite competitively, and the 2ms response time and low input lag was very desirable. However, my needs have changed and I think an IPS or 120hz display may better suit my current needs.

I'm looking to get a second monitor, but I'm unsure what to get. While I do game (somewhat) competitively, I primarily use my PC for homework, web browsing, casual gaming, and will soon be using it for programming and (basic, non-professional) video editing.

I have no real-world experience using IPS or 120Hz. I'm looking for something that's VERY easy on the eyes. I typically stare at my screen for 5-10 hours per day, and would prefer a display that doesn't strain my eyes, is less prone to cause headaches, etc.

The monitors I'm currently thinking about for each respective category are as follows:
IPS: Dell U2312HM - $230
60Hz TN: Asus VH236H - $160
120Hz TN: Asus VG236H - $330

A cost-effective solutions is important to me, which almost makes me want to immediately rule out the 120Hz monitor; not just because of the monitors cost, but because of the money it would take to keep all my games playing at 120 fps (more or less) for the years to come. The 60Hz TN is the cheapest and would match my current monitor, which is pretty attractive to me. The IPS display is the one I'm currently leaning towards--it's not *that* much more expensive than the TN panel, uses LED lighting (my GTX 480 gives me enough heat as-is), and proves advantageous in pretty much every way in terms of the actual display. My only concerns are response time, input lag, and ghosting. I mainly play RPG's, MMO's, and RTS's. Diablo 3, Guild Wars 2 Beta, and StarCraft 2 to name a few. Occasionally, I'll play CS:S, CoD4
, and other FPS games.

What advice can you guys offer me?