Any breed here at HEE has the same chances to be a "good one".

It always depends on what YOU want to breed for or how YOU want to play the game. HEE has many different ways to play - and each one is the right one ;)

But to start with my old an proven advise for new stables:

Each rider can train / ride / show up to 10 horses.
So especially for newer stables it is important to safe money and keep the weekly costs as low as possible.

You can do this by using only all discipline riders and assign as many horses to them as possible. So you keep the costs low and they still earn a pretty penny, because riders count less than 10% in the show results.
Using single discipline riders with only 1-5 horses assigned to each cost way too much for a new stable!

When you start off your stable, you should try to get e.g. one level 4 rider and buy / assign up to 10 level 4 horses to him.
You can find such horses quite cheap ( <5k ) in the horse sales.
It does not matter if those horses are mares / geldings / studs and it does not matter which ratings they have as long as they have the right level and are cheap. Additional you can hire a level 5 rider and assign up to 10 level 5 horses to him.

Stay away from capturing in this time!
They are only level 2 and take up to 6-12 weeks training before they will start earning money for you!
99% of the captured horses are lower than SSS rated and will take 8-12 weeks before they earn any money!

Then show and train those leveled horses for 1-2 months to build up decent funds for your stable. If you have some PEP+ mares among the show squad, you can brood them out in these first months.

After some weeks you should be able to buy another barn, build up more show stock and earn even more money to get you some really decent and high rated & colored breeding stock!

In this time you can learn about the differnt breeds, the differents ways how to play and which features the game offers. And once you have more than 3 barns and are settled, you can start play the game in any way you´d want to!