PUBLIC IP = 83.87.213.240 (http://ipecho.net/plain)
HTTP_CLIENT_IP = N/A
This will fetch the IP address when the user is from shared Internet services.

HTTP_X_FORWARDED_FOR = 216.73.217.14 (an External Ip Address)
This will fetch the IP address from the user when he/she is behind the proxy, can be more than one address.

HTTP_X_FORWARDED = N/A
HTTP_X_CLUSTER_CLIENT_IP = N/A
HTTP_FORWARDED_FOR = N/A
HTTP_FORWARDED = N/A
REMOTE_ADDR = 216.73.217.14 (an External Ip Address)
This contains the real IP address of the client. That is the most reliable value you can find from the user.

HTTP_CF_CONNECTING_IP = 216.73.217.14 (an External Ip Address)
This contains the IP address when using Cloudflare as a stacked CDN or proxy.

REMOTE_HOST = N/A
This will fetch the hostname from which the user is viewing the current page.