Careers can level your horse, but training and shows are much quicker. If your horse is already high in a career you can make a bit of PS, but it is much easier from doing shows rather than that.

I can offer you how I handle leveling.

If a horse is in the lowest areas of training (level 1 foundations and level 1 locals), my horses often earn much better leveling points through careers (I do not use Model, I have Education and Working Draft). The horse's personality plays a fair part in how they do in careers. But aside from that, I find that careers work best for foundations and locals and then somewhere in the state, regional and national level, sometimes slow level earners in careers do better in shows and I switch them over. Foundation, Wild and Custom horses, I can get into the 45 to 65 levels areas by the time they're 18. That's a decent enough overall, even for single star stock.

Currently, I'm also finding that explore is earning some decent first levels, so you could, theoretically, find some levels there first and then when they train up a little, switch them over to a better point-earning system.

Purebreed and Crossbreed horses that are 3 star or better, often learn best levels in halters, until they're somewhere in the Elite and Universal area. Any level 2 and up ends up doing best in shows. With the exception of 5 star halters. Sometimes they're just powerhouses in halters.😂

So, horses 3 star and up, still in low training areas, do the halters. Unnamed crossbreds, you'll only have two options, shows and explore, I'd suggest explore until they're at least local level. But, you can certainly try each of them, just use their history tab to keep watch over how many points they earn. Halters and Careers you can enter up to 5 times and shows up to 10 times. So two shows should 'add up to' a single show of Halter or Career. If one beats out the other, then use the one that beats it out, your horse will be earning more points there instead.

Hope that all makes sense. 😁

Good Luck!