What is the best armor for an acrobat in oblivion

The best armour for an Acrobat would be light armour of some variety. Generally the lighest possible armour would be best, but as you advance in level this would be poorer for combat, by upgrading your Light Armour and Sneak skills though you should be able to get the most advanced Light armour you can acquire though (which will also be the heaviest) and be able to wear that without any penalties to stealth due to the abilities granted by the high Sneak and Light Armour skills.