To make it simple the rule is don't use a bristle brush in acrylic paint but you can use a synthetic or bristle in oil based.
Purdy are a good all rounder, you can apply emulsion, WB and OB top coats to a really good standard.
Picasso are very good for WB and cut a good line when emulsioning and hold a lot of paint, havn't used in OB
Wooster FTP are popular amongst a lot of dec's but havn't used them myself.
Corona are excellent but not yet available in the UK, the best i've used for applying acrylic u/c and gloss and satin, you may be able to find them on ebay, cost me a lot to import from the states.
I don't like hamilton, blue purdy, harris and generally any cheap brush but do keep a couple as a throw away option for stuff like bin.
I don't mix mediums i have WB brushes and OB brushes. If you're going down the OB route it would be worth getting a brush mate 4 for storage.
Acrylics, dampen the brush before use and clean it periodically if using for a long time to stop dried paint forming above the ferrule. Crud cutter do a good brush restorer/cleaner.
Adding floetrol to WB and owatrol to OB keeps the paint open longer and eases application.
If your not a pro that earns his money from his brushes i'd say go with a purdy box set of monarch elites because they do everything well. Probably wouldn't bother with bristle because until they're worn in they shed a bit and the tips break which is annoying. If your going to go all WB'd i'd buy a 3 inch, 2 inch and 1and a half inch picasso.
