no matter which one you choose, you will need a breakout cable (check wiki).
You can always go for what you have now, a regular video card and use a software to drive it down to 15khz (make sure that your card is listed on the supported card list).
Some don't like using a regular one cause of the BOOT/POST of the PC (but there are ways of fixing that).
AVGA = Make life easier
VGA = Needs tweeking and time to make work.
It's really up to you. Read more about it in the WIKI about using a regular card vs avga card.