Quick and dirty guide to farming halos effectively, as well as a run down of how to build combo's in general.
The best location for farming Halo's is the "Defeat All Enemies" Alfhiem in chapter II, located on a small bridge before the final Courtyard battle, I'll upload a screenshot at a later date.
This Alfhiem allows very high combo's (to the point where not only will the multiplier be maxed out, the actual combo number will exceed the digits as well)
But why this spot in particular? If you fail an Alfhiem, you'll still get any halo's you've accumulated from your combo. Simply let the last enemy hit you, and you can redo the Alfhiem until you have all the Halo's you could want.
Building the Combo
Actually getting a really high combo is something that you'll probably want to know as well, I'd imagine.
Obviously, the most important thing is not letting the combo drop, you have about four seconds, depending on your last attack, to keep it going. Using hte shoot button, or dodgeing while having an attack button held, will help you maintain hits for the combo. Taunting and enemy will also extend the combo, or rather freeze it.
After that, you need to know what attacks and moves to do in order to maximize your points. First, the majority of weapon charge attacks will not add to your points, that is, when you hold the attack buttons you could shoot your guns, create mines with Durgha, charge up a powerful slice with Sharuba, and so forth. These moves are very useful for racking up damage and hitting distant enemies, but provide very little or even no points, so avoid using these abilities.
Next is diminishing returns, preforming too many normal style attacks on enemies in a row will cause the points from those attacks to diminish. This starts at your sixth hit, and continues from there all the way until each hit is only worth a single point. Hitting an enemy with a wicked weave will reset this. Heel Stomp is a good idea if you notice you've gone too far. This doesn't affect all attacks, but should be managed regardless.
Hitting multiple enemies with a wicked weave will multiply the points you get for each consecutive hit, but don't spam wicked weaves, as they are point-inefficient under most circumstances.
Speaking of multipliers; attacks durring Witch Time and against Enraged enemies both multiply and points you gain by 1.5X and they stack. Does not apply to torture attacks, however. Naturally, you want to equip the Gaze of Despair. Note that a perfect parry with the Moon of Mahaa-Kalaa will provide more witch time than Bat Within does(which in turn lasts longer than a dodge witch time), and will trigger witch time against many atttacks normal dodging and bat within won't trigger on.
Torture attacks are best used against almost dead enemies, to maximize the points you squeeze out of them, they will also force most enemies to drop any angel weapon they happen to be holding.
Angel weapons produce a very large amount of points compared to the damage they do; a ridiculous ammount. Though this does vary from weapon to weapon, and depending on the attack mode.
The Whip, Kulshedra, can be nearly as effective at generating points as angel weapons are, under certain circumstances. If you hold the attack button whilst hitting an enemy, and push the analog stick towards yourself, you can swing the enemy around yourself, hitting nearby enemies and generating a lot of points; comparable to the poledancing angel weapons without the need for an angel wielding it. Not all enemies can be grabbed like this, and the hitbox doesn't always want to connect, but it is among the best non-glitched methods of scoring points without using an angel weapon.
The Actual Fight
The previous section turned more into a general combo guide, and indeed the info will help you build combo's anywhere in the game. (Though there are probably many things that could be added to it)
In regards to this particular farming location: Equip the Moon of Mahaa-Kalaa and the Gaze of despair if you have them. Equip the Kulshedra on one weapon set, and prefferable the Scarborough Fair on the other set. Try to activate witch time and use the Kulshedra swinging attack on the first wave of enemies. After that, damage and preform a torture attack on an enemy with a poledancing weapon, then activate witch time and use it. Make sure to shoot enemies occasionally while waiting for an oppertunity to activate witch time, but don't use any big attacks outside of witch time. Repeat this tactic, perhaps switching back the the Kulshedra attack if the oppertunity arises until the final enemy spawns. If you have an angel weapon left use it on him, else just hit him normally till he's almost dead, but instead of killing him simply let him hit you until you fail.
Using this method, you can generate up to 700,000 halo's in a single run, and be ready to do another one instantly. No need for glitches, no need to unlock the Climax Bracelet or whatever else.