The right brush makes a hard job quick and easy.  But you need more than one.  No one brush will cover everywhere.  You don't need hundreds of brushes, but you need a few good ones, and be willing to swap as you go.  If you spend ages trying to get into little bits on your wheels, and get you finger out to get the corners then you need to get more brushes.

We have a huge range but if I was starting out detailing I'd get 1 of each detail style brush, except the boar hair, Id get 2-3 of those as I'll use them on wheel nuts, engine bays, interior, and I'll want to keep them separate to be efficient and not cross contaminate and make a mess.  It get the  toothbrush, you don't use it much but when you do you need it, I'd get a soft and hard barrel brush, a soft and hard short wheel brush, a per hair brush (Neighbours cats sleep on the roof of my convertible) and a pack of wheel woollies, they are expensive but worth it, they are forged to the rod and really work well, I use the small one heaps on my tight wheel gaps.  Id use a stiff short brush on the tyres or rubber floor mats.

If I had shiny black interior plastic Id have the ultra soft detailing brush.  For cleaning carpets I use the drill brush and the hard carpet and pad brush, I'd also use the latter on white wall tyres.  While you can clean pads with this its much faster with the pro pad brush though.  

Those are my go to's but its great to have a range.  Most of our kits have the brushes I'd use in them.  

 With brushes there is a trade off of aggression and softness.  All brushes scratch a little bit, but a brush like the hard barrel brush is more aggressive, it will also clean much faster than the gentler soft barrel brush.

 I would not recommend using brushes on the main panels of your car.