What is the difference between a segwit address that starts with a 3 and a b?

[Mountaingoat]

I have a few questions:
What is the difference between the two addresses?
Are they both Segwit?
Which one is the most recent version?
Which one is better to use?

[Xynerise]

Segwit addresses that start with 3 are P2WPKH nested in P2SH.
(Not all addresses that start with 3 are Segwit addresses, they could be multisig addresses.
There is no way to tell the difference between the two until the address spends funds.)

The ones that start with bc1 are Bech 32 called "native segwit" in Electrum.
Defined in BIP173 by Peter Wuille
https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki

Bech32 transactions are 38% smaller than legacy (standard addresses that start with 1) transactions, while P2PWKH-P2SH transactions are 27% less than legacy transactions of the same number of inputs/outputs.

Unfortunately bc1 is not backwards compatible so users have to upgrade to a wallet with Segwit support to be able to send funds to this type of addresses.

[Mountaingoat]

What does bc1 mean? Is that the address that starts with a 1?

Another question, can you make a vanity Bech32 address like with the adressess that start with a 1 or is that not possible?

[achow101]

What does bc1 mean? Is that the address that starts with a 1?

It's the beginning of every bech32 address, the ones that start with a "b".

Another question, can you make a vanity Bech32 address like with the adressess that start with a 1 or is that not possible?

Yes. You can make a vanity address with any type of address.

[Mountaingoat]

What does bc1 mean? Is that the address that starts with a 1?

It's the beginning of every bech32 address, the ones that start with a "b".

Another question, can you make a vanity Bech32 address like with the adressess that start with a 1 or is that not possible?

Yes. You can make a vanity address with any type of address.

How can I make a vanity Bech32 address? Are there any guides you can link me?

[achow101]

How can I make a vanity Bech32 address?

The same way you make a P2PKH vanity address (begins with a '1'); generate random private keys, calculate their public keys, hash the public keys, and encode it using bech32. You will need some software that can do that, but I don't know of any that currently exist.

Are there any guides you can link me?

No.