Quickfire Stealth vs Das Ultimate? (Both with brown switches) They both have PS/2 which gives better latency if I am correct? The Das has better stabilisers or something that makes it feel more like a mechanical keyboard.
1) It boils down to taste, I think most people on the board here would recommend Quickfire (in general) for first mechanical keyboard. Das keyboard may look nice but that is more or less it. I read Das keyboard uses ABS (common as hell) plastic and am not exactly sure on Quickfire's keycap material.
2) PS/2 gives lower latency yes but that does not necessarily mean that it is superior completely to USB. If you have read through the link that I posted on PS/2 and USB you would have noticed there was a big talk about it. However one still needs to question at the end of the day is PS/2 really all that much worth it in their case. There are professional gamers with mechanical keyboards but are using USB. I am talking about Korean Starcraft players for instance. The funny irony is that I don't think they would be willing to contemplate on using dated PS/2 technology just for lower latency. USB protocol has much higher bandwidth than PS/2 (theoretically), provides more power than PS/2 and is more durable (in general) than PS/2.
I personally do not believe most average people would benefit that much by switching from USB to PS/2 apart from the few possible scenarios where PS/2 is definitely required. Otherwise the lag as mostly noted is only worth 1 milliseconds if speed is such an important issue.
3) Not sure on better stabilisers but I do know that within the Cherry MX realm the talk has always been on various stabilisers such as Cherry vs Costar. However the bottom is that most people still generally recommend Quickfire for beginner's board. That must also mean that when choosing Quickfire you may get better support coverage.
4) The "feel" of mechanical keyboard is often a disputed taste over switches/forms. There are up to as much as a dozen different switches floating around and there would be various people that would recommend X over Y. Ideally for any beginner is to start something that has been recommended by those who probably would have tried more than one mechanical keyboard. Unless you had a keyboard you wanted for a long time like I did and you have been firm on reasons for choosing a specific board - you are better off choosing a recommended one by others in general.