Tydil has a pretty good outlook on it
Budget and proficiency play a big part in the selection. When you start out, you tend to be a little rough on brushes, and tend not to have the patience to do the little things to keep them tip top -- no paint in the ferrule and no dried paint on the brush are then top two.
Plus, synthetic brushes are stiffer and easier to learn on.
I also think everyone should learn how to use flat and filberts properly, as they make a big difference in getting a nice coat on, and for blending in certain situations.
Once you really enjoy the hobby, you owe it to yourself to own one set of nice brushes; it does make a big difference and ups your game a notch, and it's just plain more fun.
Personally, my go-to rounds are Winsor & Newton Series 7 sizes 1, 0, 00. I own a zillion other brushes but these, plus some flats, account for the bulk of my painting.