What is the difference between Bitcoin Core and UASF? I am a little confused about what the actual difference is between Bitcoin Core and UASF, are they both only for SegWit?

If so who is then for SegWit2X?
Correct, core and UASF groups are both Segwit supporters (as are Segwit2x supporters).  Both core and UASF are against 2x.  UASF is just an attempt to force segwit if miners had rejected it (miners did not reject). I'm not really sure how they expect UASF could have been successful without hash power if miners had actually rejected Segwit.

I've seen some core supporters argue that UASF was reckless (would have disrupted non-Segwit nodes), so though the chains they support today are the same, the groups are not perfectly in alignment.  More details here:

https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-April/014152.html

You can see who supports the New York Agreement (Segwit2x) here:

https://medium.com/@DCGco/bitcoin-scaling-agreement-at-consensus-2017-133521fe9a77

As stated in the link, they represent (at the time of the agreement):


58 companies located in 22 countries
83.28% of hashing power
5.1 billion USD monthly on chain transaction volume (likely larger now with higher price)
20.5 million bitcoin wallets


Most notable from my perspective are Bitpay, Coinbase, and the majority of miners.

Here you can also find those who supported the original Hong Kong Agreement from a year ago:

https://medium.com/@bitcoinroundtable/bitcoin-roundtable-consensus-266d475a61ff

The original HKA failed.  Many who signed onto the HKA (e.g. Adam Back of blockstream and the core contributors) seem strongly opposed to 2x today, which is most of why it failed. The Segwit2x of NYA is in some ways an attempt to bypass those who agreed to pursue 2x a year ago but who actually ended up fighting it.

Opposition (the core devs, who effectively want to retain veto power) argue that giving in to miners/businesses gives them too much power.  Some from the 2x crowd argue blockstream &amp; core are attempting to block capacity increases to force users into the lightning network. It's all rather political and there isn't much trust.  Ill will is taken for granted in most debates.

The HKA was a bit less committal ("This hard-fork...will only be adopted with broad support across the entire Bitcoin community") which I suppose is how the core team can say they aren't technically violating their word.

My impression is that these particular core HKA signatories are the primary driver of "the Bitcoin community" that opposed.  When it became clear that core had no intention of pursuing 2x and were actively fighting it, the initial HKA compromise no longer seemed relevant or in good faith -- i.e. activating Segwit would sacrifice any near-term opportunity for a meaningful capacity increase. Blocking Segwit became a tool to fight for a capacity increase. All this further fanned the flames of the rather toxic scaling/capacity debate.

Here's a list of companies tracked by coin dance that support or oppose segwit2x, though the data is a bit sparse. As of today 67% are neutral, 24% support, and 9% oppose. I don't recognize many of the "no" voting companies other than blockstream. They give the option to weight the votes by total web traffic (not perfect but gives some indication of relevance), bringing support to 44%, neutral to 56%, and opposition to nearly zero.

https://coin.dance/poli