You will note that some Enta resellers just use Enta for phone support, whereas others (ADSL24 included) use their own phone support, meaning you have direct communication with the reseller you sign up with (as well as Enta if you want to call them - 0870 number though)
We use an 0161 number for sales and support and are based in Manchester
The main other differences as others say is web/e-mail/control panel facilities - again most resellers use the Entanet control panel where others (ADSL24, UKFSN etc) have developed their own.
If you have any questions please ask.
James