When you print a light color on a dark fabric there is no difference between the two inks, however you must follow a special procedure: (you can choose one of these)
1) - Print a white base on the fabric and then print your final colour on top of this base
2) - Print your image, dry quickly using a hair drier (without lifting the t-shirt from the table) and then print the same colour again.

What is my advice?
If you can buy a good drier (cost about Euro 5,500.00) you can use both inks depending on the final image required.
Without a drier, water based inks are certainly better. And there are two tricks you can use to delay the drying time on the screen:
1- Add a ritardent to the ink (maximum 2-3%)
2- Moving the squeege in a particular way to ensure that the image on the screen is always covered by the ink. The image must always be loaded with ink.

To be honest there are some driers which, although not designed for this purpose, nevertheless can be used.
For example: a flash drier, which costs about Euro 1,300.00, or a thermal press, which costs about Euro 500.00.
The disadvantage is that it slows down the production time. If you work for love, you can do it; but if you work for business, that's not a good idea.
With regard to the emulsion: a good universal emulsion is suitable for both inks; you can find them at this address: http://www.screenprintingstore.net/universal-emulsions.html