Here are the best methods. It is best if you mine with the floor at y-15.
Bed Mining
Bed mining is is one of the best and cheapest ways to mine netherite.
Advantages
- Easy to detonate
- Rather cheap
- Large explosion uncovers more blocks
Disadvantages
- You need to be careful not to blow yourself up
- You may take some blast damage
- Lots of fire everywhere
Resources needed
- A lot of beds (Preferably a full inventory)
- 2-3 stacks of a blast resistance material (Preferably basalt)
- 3-4 stacks of a scaffolding block (Preferably netherrack, as you can get lots of it while mining)
- A diamond or netherite pickaxe to clean up or mine debris
Optional Resources
- A few fire resistance potions
- Blast Protection armor
How to do it
- Mine a hole or staircase down to y-15.
- Place a bed 6 blocks from the end of the path to the surface.
- Place your blast-resistant block in front of you.
- Right-click the bed to blow it up.
- Take a look at the crater, and search for ancient debris (This is what you're looking for)
- OPTIONAL: Pick up the netherrack and put out fires to regenerate your amount of scaffolding blocks.
- Bridge over with your scaffolding blocks
- Dig 6 blocks in again.
- Repeat 2-8 until you run out of beds, or are satisfied with your mining.
Yields
- Average 0.6 Ancient Debris per explosion
Bubble Mining
Bubble Mining uncovers a lot of blocks, and can be fun to use.
Advantages
- Very thorough
- Not very resource-intensive
- Satisfying to insta-mine
- Many resources are gathered as a side-effect
Disadvantages
- Causes strain on hands after a while
- Many trips to repair pickaxes are required
- Lava is VERY dangerous here
Resources needed
- Some diamond or netherite pickaxes (Preferably enchanted with Unbreaking III, Efficiency V, Mending)
Optional Resources
- Some fire resistance potions
- A beacon with Haste II
- Pickaxes enchanted with Silk Touch
How to do it
- Dig down to y-15.
- Hold down left-click or spam it, while turning around slowly to uncover all blocks.
- Once all blocks in range are mined, move 3-5 blocks forward.
- Repeat 2-3 until no pickaxes left, all are almost broken, or you are satisfied with mining.
Yields
- About 40 Debris per hour, net worth 39.7 per hour (Yields - Expenses (Pickaxe))
- Lots of stacks of other resources
End Crystal Mining
Massive explosions in the Nether reduces amount of digging and placing
Advantages
- Not much crystals needed
- Uncovers many blocks
- Easy to detonate
- Can be detonated from a distance
Disadvantages
- VERY expensive
- Lots of obsidian needed
- Hard to clean up
- Easy to blow yourself up, massive amounts of damage to entities near the crystal
Resources needed
- As many end crystals as you want
- Just as many obsidian as you have crystals
- A bow (Preferably with Unbreaking III, Infinity)
- A diamond or netherite pickaxe to clean up or mine debris
Optional Resources
- Bow with Power V
- Several stacks of scaffolding blocks
How to do it
- Go down to y-15
- Dig 10 blocks away
- Place obsidian on the floor of that tunnel
- Place end crystal on obsidian
- Run 10 blocks back
- Shoot the crystal
- Scout and mine debris
- OPTIONAL: Collect netherrack and put out fires to regenerate scaffolding blocks
- Repeat steps 2-8 until you run out of crystals or you are satisfied with mining
Yields
- About 0.8 Ancient Debris per explosion
TNT Mining
One tap blows it all up, lots of uncovered blocks.
Advantages
- Relatively cheap
- Many blocks uncovered
- One-tap detonation
Disadvantages
- TNT can fly about and land in bad places
- You could blow yourself up
- Some TNT may not ignite
- You need to dig very long tunnels
Resources needed
- As much TNT as you like
- Flint and Steel or a Bow with Flame
- Diamond or Netherite Pickaxe to dig tunnels and harvest debris
Optional Resources
- An Elytra with a few rockets
How to do it
- Dig down to y-15
- Create a 1x2x1 tunnel in one direction until you are satisfied.
- Place a TNT at the end of the tunnel.
- Go two blocks back.
- Place another TNT. Each space should look like this:
Key: T = TNT, S = Air space, ... = Continue this pattern
... S S T ...
- Repeat steps 3 and 4 until you run out of TNT or return to the starting point. It should now look like this:
... T S S T S S T S S T S S T S S T S S T ...
- Go to the end of the TNT chain and light it on fire with flint and steel or a flame arrow.
- Be careful and go to a safe spot to watch the detonation.
- Ignite any surviving TNT.
- Scout and mine all debris found.
Yields
- About 0.4-0.67 Ancient Debris per explosion
- About 10 Ancient Debris per 64 blocks of TNT
So far, all of these are pretty good ways to mine netherite, just look for which one is the most satisfying or easy! I hope this helps!