Interesting replies but only one (unless I missed it) mentioned using a soft wide brush. Bigger brush the better generally and if you can use Sable. Expensive I know but will produce excellent results with no brush marks.
Another aspect that hasn't been mentioned: Cleaning.
In the Art world when using Acrylics it's recommended that you clean brushes first with white spirit followed by warm soapy water then rinse well and dry. Never leave a brush resting on bristles.
These are Gnot my comments BUT come from the leading Art Society in UK - SAA.
By the way there are a Baker's Dozen of different Brush types of which I use the following: Round, Riggers, Flats, Mops and Hake. I also have a Scrubber brush somewhere, hardly an item for modelling though. I've not tried it - it could be used to remove paint from area to reveal underpainting.
I guess I'll get some
comments from that lot