if you are looking at having to use a tft screen for your cabinet then just go for the largest size you can fit in (19" is equivalent to a 20" crt), with the fastest response time (12ms or better) and the widest viewing angle you can find.
however from personal experience I can say that a tft screen just does not compare with a decent arcade monitor. (currently using my 20" tft in my cabinet after my arcade monitor fried...... I want the arcade monitor back) the tft screen although it is crisp and clear it just doesnt look right at all.