What is the best horse in Oblivion 4 The Elder Scrolls

Each horse is different, so the best is either the unicorn which can't be a default horse, or the Shadowmere which can be a default horse. The unicorn is the strongest and the 2nd fastest. The Shadowmere is the fastest.

The Best buyable horse in Oblivion is the White Hourses (Cheydinhal stable).