Yep, all three are e-IPS panel monitors. Not necessarily a bad thing.
For gaming most people TN panel monitors because they have the fastest response time of 2ms. "Slower" TN panels are 5ms. The Dell U2412 is 8ms, the HP ZR24W is 5ms and the ZR2440 is 6ms. The ZR2440 more expensive than the other two, but it's just there as an option.
Overall response time is not a very scientific way to determine how good a monitor is for games. I will say that generally speaking the lower the response time, the lower your chances of seeing ghosting. But it's not as simple as saying a monitor with 4ms response means you are twice as likely to see ghosting compared to a 2ms response time monitor. Or 6ms means 3 times as likely as 2ms.
Response time is basically measure by how fast the pixels can change from one shade of color to another. Only the fastest time is used and all other times are tossed out with the trash. Also every brandname has a different methodology to measure response times. Therefore... not scientific as I stated before.
I have seen some test results where the fastest time for Monitor A is 2ms and the slowest time is 325ms, while Monitor B's fastest time is 5ms but the slowest time is 300ms. So which one is actually the faster monitor?
The best advice I can give is to go to the Display Comparisons section of each of the reviews and look at the PixPerAn test screenshots; the race car driver saying "I need more socks". Compare the images to determine which one seems to have less ghosting.
TFTCentral doesn't really review many TN panel monitor. The most recent TN panel monitor they reviewed was the Samsung SM245B back in Oct. 2007. So... unfortunately it's not very recent. The link to the review is below. Again look at the PixPerAn test screenshots and use them to help evaluate if one of the two monitors you have chosen would make a good gaming monitor.