Greed Sever (ground hit)
As long as you do this early enough, this is guaranteed. A somewhat delayed burst can be blocked, however. This is also a usual point where I see players panic burst, and because of what Ky can get off it against many characters, it's not the worst place to do so. Bursting on ground hit is key though; bursting while hit in the air, such as right after 3H xx GS, will almost always lead to a whiffed burst high in the air.
HS Vapor Thrust (ground and air)
Bursting against ground HSVT is a prime example of a type of burst (specifically, hit burst) that Nage talks about in his post about his personal blue burst philosophy. While bursting before this would negate a lot of the damage you took in this combo, many of those spots are risky due to Ky being able to hard bait them or are just burst safe. In the case of bursting against HSVT (in an example of it leading to knockdown, say after something basic like 6P c.S 2H HSVT), you don't negate the damage, but you're guaranteed to negate the opponent from starting their oki game.
6P (ground hit)
You'll probably rarely see 6P used in a ground combo, but it's a guaranteed point nonetheless. Bursting here avoids some decent damage ground combos that can lead into strong oki, such as a string leading into 6K xx Split Ciel, microdash 2D xx CSE.
6H (after first hit)
This is a shakeup from pre-REV2. Bursting after the first hit of 6H used to be a death sentence; Ky could just hold back, block and get a free punish. But in REV2, the gap between the first and second hits is large enough to burst inside of. This is a key point to burst at, due to the fact that any combo with 6H in it is going to lead to high damage. Do note that if your burst is delayed, Ky will recover from the second hit of 6H in time and block.
Stun Dipper
This is another example of a hit burst, used to safely negate okizeme. Bursting after either hit is fine, although it's much more preferable to do so after the first hit because it negates a little bit of damage. It's important to note though, in case you get burst back after the second hit and want to get out.
3H
This will always leave Ky at a range in which he is in range to get clipped by your burst; no option that he always has access to will be able to bait it. 3H will almost always lead into Greed Sever or Vapor Thrust on hit, so bursting here will help you avoid taking high damage from their follow-ups.
With that said, there are some riskier points you can burst at, but be cautious, as these aren't completely guaranteed and can be reliant on one's reactions.
After 3H xx Greed Sever, right as you touch the ground
This is a very specific point, but for one big reason. If Ky does HSVT after landing, your blue burst will whiff, but Ky will also fly through your body, and you will land before him. Depending on your timing, you can get almost any starter you want against him. There are two big risks involved with this, however.- You're sacrificing the burst meter that you get back from hitting it. Depending on the situation, this may not matter much (mainly if you're going to kill Ky with whatever combo you're going to do), but you have to weigh the risks of the damage and momentum you'll get from your punish versus that burst meter that you won't have, especially if you haven't won a round yet. I would usually recommend going for it if it guarantees you the round, however.
- Ky can also forego ground HSVT after Greed Sever. A personal note is that versus light weights and medium weights (which is the entire cast sans Leo, Johnny, Bedman, Potemkin and Haehyun), I prefer to just go for super jump j.S j.H air VT afterwards, because I usually cannot get a knockdown afterwards against them unless I'm in the corner vs a medium weight. As long as it's inputted correctly, this will also block burst. Against the heavy weights, I usually go for the super jump combo if they have burst, because of the risk of whiffing VT. But again, this is all personal philosophy; any other Ky player that you play against could have a different approach to this situation.
Between c.S/5H/2D and a cancel into a special move at close ranges
For Ky, this is usually between one of three options. Stun Dipper, Split Ciel and Charged Stun Edge. If he has 50%, 2D xx Sacred Edge is common to see as well, and this can also be bursted against due to Ky's hurtbox extension; however doing so is a guess because you have to burst before the super flash. If you feel that you can react to Ky doing something off this, it's usually a good point to burst. However, Ky's spacing is key to your choice of bursting. If he does Dipper, then you should always hit your burst, but a well-spaced Ciel or CSE can end up causing a whiffed burst. It's also very key that you react to this, as these normals are common places that a Ky player will hard bait for burst, with either a jump cancel off c.S/2D or nothing off 5H.