Quoting Noah Davidson
Not dangerous under circumstancs, banthas and reeks are still wild animals and, as such, can be unpredictable. Banthas are smarter than reeks andare easily domesticated. This means they can be trained to attack on command, whereas a reek will most likely strike if startled or threatened.
In this fight, the contestants would literally butt heads. Neither the eek nor the bantha builds a strategy around suprise attacks; each would announce its charge with a lot of snorting and stomping. The repeated thunderclap of horns colliding would wear each animal down, turning this fight into a grueling endurance contest.
I, personally, think the Reek would win. It's too deadly to lose to such a docile creature like the bantha.

Quoting parker declue
my words exactly because the reek has long horns