Ranger Animal Compaion

[j_spencer93]

So I have a player interested in playing a Ranger (revised) but wants to know what all his options are for an animal companion. The revised ranger doesn't seem to follow the older 1/4 cr rule so i am not 100% what to tell him.
Should i let him have CR 1/2 or lower beast or keep it at CR 1/4 and just add the few oddballs the revised threw in there?

[Specter]

"As a rule of thumb, a beast can serve as an animal companion if it is Medium or smaller, has 15 or fewer hit points, and cannot deal more than 8 damage with a single attack. In general, that applies to creatures with a challenge rating of 1/4 or less, but there are exceptions."

This is what the UA says. But I guess it's more of a master-player agreement; a horse is not a medium creature, for instance, but if you toned it down to that I guess it would make a good companion.