When choosing a brush to use for oil colour, you need to think about a brush with hair that is able to move thick, viscous colour e.g. Hog hair. However, if you plan to use thinners to alter the properties of the colour you will then need to consider using another type of hair e.g. Sable hair.
Acrylic colour can be used in viscous form or in a thinned down form, similar to (though not exactly comparable to) water colour. The brush you select will depend on the style and technique you use and whether you need to move full bodied colour or control flowing colour.