Meditate requires leather armor or mage armor in order to function. Each 10 points of meditate grants one extra point of mana recovery.
Focus works with any armor. Each 20 points of focus grants one extra point of mana recovery. Each 10 points of focus grants one extra point of endurance recovery.
Thus if your primary interest is in mana recovery, and using leather/mage armor is not a problem, meditate is the better choice. You need twice as much focus points to get the same mana benefit offered by meditate. However, meditate does not help endurance recovery at all. Generally, focus is considered the recovery power for warriors, while meditate is considered better for magic users.
Note that if your character is human, the JoaT (Jack of all Trades) racial characteristic gives you an effective 20 points in both meditate and focus. You need more than 20 points of real or jewelled skill in either to get above what JoaT offers for free. Thus it is likely that a jewel offering 10 focus would have no effect at all on your recovery rates.