I'm trying to host my website from my Raspberry Pi 2 which I will be using as a headless server that I will ssh into. I want to install Ubuntu on it.
Should I use this download link which is from the Ubuntu for Raspberry Pi webpage?
Or should I use this one from the Ubuntu Server installation page?
I am also unsure what the differences would be and would like to know what they are.
Raspberry Pi preinstalled Ubuntu 20.10 Desktop and preinstalled Ubuntu 20.10 Server images are available from ubuntu.com. The preinstalled images allow you to unpack a preinstalled version of Ubuntu onto a target device.
Download the first link in your question. It is the official Ubuntu 16.04 image for Raspberry Pi 2 at the ARM/Raspberry Pi - Ubuntu Wiki webpage. The instructions for installing this image are at the same webpage.
armhf
Raspberry Pi 2: ubuntu-18.04-preinstalled-server-armhf+raspi2.img.xz (4G image, 402MB compressed)
Raspberry Pi 3B/3B+: ubuntu-18.04.2-preinstalled-server-armhf+raspi3.img.xz (4G image, 419MB compressed)
Raspberry Pi 4: Ubuntu 19.10 Raspberry Pi 32-bit and 64-bit preinstalled images (raspi3) now support the Raspberry Pi 4 platform out of the box. You can install Ubuntu Server + desktop environment (optional) on a Raspberry Pi 4 by following the instructions in this answer.
Further releases can be found at http://cdimage.ubuntu.com/ubuntu/releases/. Please note that even though these images are labelled "+raspi3" they are compatible with the Raspberry Pi 2 and 3 (and 4 in the case of 19.10 and later.
arm64
Raspberry Pi 3B/3B+: ubuntu-18.04.2-preinstalled-server-arm64+raspi3.img.xz (4G image, 419MB compressed)
The generic arm64 ISO images can be used with the Raspberry Pi 3. Instructions for booting these are here.
Login username is "ubuntu", password is "ubuntu". You will be asked to change the password on first login.
Update: Canonical has released official [Ubuntu Core 16 and Core 18 images for Raspberry Pi 3. The instructions for installing it are at Install Ubuntu Core on a Raspberry Pi 2 or 3. As the wiki says: Snappy Ubuntu Core is a new rendition of Ubuntu with transactional updates - a minimal server image with the same libraries as today’s Ubuntu, but applications are provided through a simpler mechanism. A new release of Ubuntu Core is released every 2 years on even numbered years (2016, 2018, etc.).
Ubuntu Core 16 is based on Ubuntu 16.04, and is supported for 5 years.
Ubuntu Core 18 is based on Ubuntu 18.04, and is supported for 10 years.
Ubuntu MATE 16.04 has fully working bluetooth and wifi on the Raspberry Pi 3.
The Raspberry Pi image for Ubuntu 14.04 is no longer maintained. Please use the more recent images instead.
Although the majority of the Raspberry Pi cloud/server image works like any other Ubuntu system, there are a few packages in all currently supported versions of Ubuntu that you may not be familiar with.
linux-firmware-raspi2 - GPU firmware bootloader files and WiFi firmware configuration fileslinux-raspi2 (linux-image-raspi2) - Linux kernel with patches from https://github.com/raspberrypi/linuxu-boot-rpi - Provides the various uboot* binaries under /boot/firmwareflash-kernel - Automatically copies the latest kernel, dtb file and u-boot script to the Pi's FAT-formatted GPU firmware partition.