Which is better?

No argument. Fighter->Mage. Do you want reasons?

If you'd be so kind, yes. [img]smile.gif[/img]

<U>Mage->Fighter Pros</u>
Limited assortment of Mage spells.
Fighter class can reach high levels.
More HP gained per level after 9.
Better THACO.
<U>Fighter->Mage Pros</u>
Large assortment of Mage spells.
Fighter class can be improved by high level buffs.
Can render opponents immobile much easier.
More HP gained during the Fighter side.

There are many more Pros, but those are the most obvious.

definetely fighter->mage
you get the important part of the fighter hp, good thac0, to take advantage of exception str(really not all that important in the long run) and all the best mage spells.

Mage/FIGHTER? It sounds like a nonsense. Why is the mage part here? To allow the mage/FIGHTER to cast a few low level spells? Also, let us note that the low level of the mage part grants inefficient casting and that the mage/FIGTER can cast only without (most of) armor.
On the other hand, fighter/MAGE makes sense. It is a mage with essentially improved ability to fight. Even if you will dual immediately at level 7 (not a good idea), your mage will be able to use any weapon and he will be able to place more '+' in the selected weapon skill. A fighter/MAGE need not contribute to final success of a fight only by casting. He can fight as well. This affects the selection of his spells - he will memorize only those spells that are useful against difficult enemies. Easy enemies will be serviced by a weapon.
Mage/FIGHTER is nonsense. On the other hand, thief/FIGHTER isn't nonsense. The low level thief part can be improved by Potions of Master Thievery. A thief/FIGHTER can be specialized in detecting and disarming traps. In the other words, a thief/FIGHER is a figher able of detecting and disarming traps and also of stealing if it is advantageous.

F/M-Multi
F/T-Multi

While I agree that fighter==>mage is the superior order in which to dual the two classes, there is something to be said for mage==>fighter as long as the dual takes place at a low level. Since the game allows you to cast spells from scrols and use wands while wearing armor, what you essentially have is a fighter who can also use wizard magic items for a sacrifice of a few hit points and xps. This wouldn't be very good in a party, but would be interesting to try in a solo situation.

What is a good level to dual?

From fighter to a mage- About Level 13-15.
Mage into a fighter- Level 13 (not really sure)