Both are good governors on the defense, but the choice depends largely on circumstance.
Victor vs Moksha (at least on higher difficulties) boils down to a question of efficient use of Governor promotions.
Once you get to Emperor+ (especially on Deity, and also when playing against good human players), you need to play more optimally, and you cannot afford to "waste" governor promotions anymore (2 in the case of Moksha, for reaching the healing promotion)
The question then is, "which of these two governors will serve other purposes that are in line with my my victory goal"?
I'll list some examples:
If going domination victory: Victor is usually the best choice when needing to defend, and he has strong compounding value also for when you later go on the offense.
His promotions are mostly quite bad (especially the final ones), but he has a very strong level 2 promotion (Garrison Commander), which is extremely useful for when you are pushing into the enemy's territory to conquer them, as it gives you an area-wide loyalty boost to all nearby cities (extremely useful for compounding loyalty on newly conquered cities).
So if you need to defend and you are planning for an ordinary domination victory, you most likely want Victor anyway for that skill anyway, and therefore you aren't "wasting" a promotion by recruiting Victor to begin with.
There is one exception though:
If you are going domination victory, and you
also have a very strong faith income (possibly also a religion), Moksha can become more valuable.
The reason for that is that his final promotions (especially Divine Architect) allows you to instantly buy a district for faith.
As newly conquered cities can often have terrible production, you can often make great use of faith-buying a Campus, Comm hub etc. to keep rapidly improving your infrastructure as you go along conquering.
Most other victories: Moksha is often a better choice for defending, as he most often has the best compounding value for further peaceful play.
I say often, because using the same example as above, you need to assess whether or not you have a strong faith income/religion to begin with.
For a Religious Victory, Moksha is a nobrainer.
You are gonna get him eventually anyway, especially for Patron Saint (Divine Architect can also be useful), and the sooner you get him to his final promotion, the better.
For Culture Victory, you need a strong faith economy these days as well, so Moksha is largely again a nobrainer as you can get good value out of Divine Architect for newly settled cities (instabuying a Theatre District for instance).
For Science Victory, you might not have a strong faith economy, so in this case the argument can be made for Victor.
The reason for this is that Victors initial defensive power spike comes from his initial recruitment where he boosts the city combat strength.
If you feel like you need more defensive power (giving additional ranged attacks, combat strength and immunity to siege), you can then keep investing further into him as needed, but if you see that his initial recruitment promotion is enough, you save those governor promotions for something better.
If you do have a strong faith economy when going the Science route, Moksha can again be a great choice that far outstrips the value you'll get from Victor (instabuying a Campus in a freshly settled city).
I was actually thinking Moksha would be better offensively. He will let me attack a neighboring city, then return to heal fully. Or if my new city is attacked, he lets me heal and go on the offensive more quickly.
Victors bonus is only useful if they come to me.
Moksha can be used for offensive plays as well like you describe, but I wouldn't waste governor promotions on him unless you happen to have a religion or a good faith economy.
Byzantium is a great example of where Moksha can be superior, as Byzantium usually invests in a religion (and thus faith) to begin with.
But be aware that for rapid pushes, Moksha's value can drop off.
The reason for that is that it takes Moksha 5 turns to establish, and if you push too fast, you might find yourself in the awkward situation where Moksha is established in a city far away from the front (as you kept grabbing more cities ahead), so you might actually have to travel back quite a bit, which becomes less and less worth it the further ahead your push is in relation to where he's established, as opposed to just healing normally in the furthest captured city.
You can of course always relocate Moksha further ahead, but then you gotta wait 5 turns before the bonus kicks in again, which might see little actual value.
The best use is usually where you have him established in a city right next to a city that you are besieging and struggling with.
In that case, he will have more than enough time to get established, while your units can move back 2-3 tiles and heal to full, before resuming the siege on the enemy city which overall makes for some very efficient play.
For rapid pushes, I prefer Victory because it only takes him 3 turns to establish and start projecting additional loyalty on captured cities, and the area of effect is quite wide before your furthest conquered cities are out of range.
Getting that extra loyalty (Victor in a nearby city, and another random governor in the freshly captured city that struggles on loyalty) can often be the difference between a city flipping in 3 turns, as opposed to 7-10 turns with Victor nearby.
In this case, having 7-10 turns before the city flips (as opposed to 3) can make all the difference for your push, as it might buy you some critical extra turns to knock down that enemy high population city that undermines your loyalty.
It has happened (and keeps happening to me) so often that I consider Victor nearly a nobrainer for standard domination pushes as you get so much value out of him for the rest of the game, for a measly 2 governor promotions.
