Both. I do SD showing, almost all those horses are mares and I use them for quests (as well as a barn of EEE+ WB mares with genetics I want to produce) so they're both personal breeding horses and double as quest horses when need-be.

Likely not the most profitable, but it's more than enough for me, and enjoyable ^^

Both.

.

If you look at my barns you'll see a number of quest barns - all of them are open to the public. You'll also see a number of SD barns, because I show and breed both (and they can be useful in quests, as well).

When doing a quest I frequently pop to Search Horses, pop in my barn number, select 'mare' + 'unbred' + the quest colour/breeding level.

Then I get a list of suitable mares from all barns in my stable yard.