To clarify, this is a Super Mario Bros mechanic question. Jump boosting (I believe that's the name) is when you to get a jump boost when jumping on an enemy. Mario's jump reaches a higher height after jumping from an enemy/object's head/top if done correctly. It's very similar to footstooling in Super Smash Bros (and obviously it was a mechanic before Smash).

In other words, what Mario does on this shell jump.

link: https://m.youtube.com/watch?v=EyggGfg3N0g

There are two ways to do this in SMB 3, NSMB series and Mario Maker:

1. Hold the jump button anytime before landing on the enemy.

2. Press the jump button the moment you land on the enemy.

In Super Mario World, 3D Land, and 3D World you can only do this by holding the jump button before landing on the enemy. Timing the moment you land on them won't work but holding a the button before will. 

Personally, I prefer option number 2: hitting the jump button the moment you land on the enemy. I feel like I can react better this way than holding on a button and then positioning Mario's feet above the enemy/projectile's head.

What method do you guys prefer?

I believe I usually go with option 1.

You can still do that in SMB 3, NSMB series, and Super Mario Maker though. But they don't let you do this in Super Mario World or the 3D series for some odd reason.

To be fair, in DKC: Tropical Freeze at the very least (can't speak for other DKC games, haven't played them), you can hold the button for the jump boost. The difference being that it can't be in the same button press you used to jump in the first place. Jump, and then press and hold while in mid air.

Ha, same here.

I am used to option number 2.Maybe its because I feel its more intuitive, and got acostumed during the many years I played Super Mario World, but I find it better.But I will admit that option 2 can feel pretty handy, and makes Mario games in general easier for people that dont like/suck at challeging levels.

I just hold it since it requires less skill :p

You guys actually prefer holding the button than timing the hit? I can't play Super Mario World and the 3D series well because I have to hold the button before landing on the enemy/projectile... Do you guys always hold the button until Mario reaches the ground then? I feel like there's too much pressure getting the position right when I need to hold the button versus hitting jump once, position, and then jump. Then again, I also feel queasy when I miss a jump and Mario falls down from a tall platform.