For general airline reviews (which might well make reference to legroom, etc), Skytrax can't be beaten:
http://www.airlinequality.com/
However neither my link nor that provided by Bednobs will be much use unless you know which airlines have direct flights from the UK to Heraklion International Airport. Here's a complete list of all services:
easyJet (ex Bristol, Gatwick & Manchester)
Jet2: (ex East Midlands & Leeds/Bradford, with seasonal flights ex Manchester)
Monarch: (ex Birmingham & Gatwick, with seasonal flights ex Manchester)
Thomas Cook: (ex Birmingham, Bristol, Cardiff, Doncaster/Sheffield, East Midlands, Glasgow, Leeds/Bradford, Gatwick & Manchester, with seasonal flights ex Newcastle)
Thomson: (Seasonal flights only, ex Birmingham, Bristol, Cardiff, Doncaster/Sheffield, East Midlands, Exeter, Glasgow, Gatwick, Luton, Stansted, Manchester, Newcastle)
There are theoretically also charter flights, operated by a number of different tour operators, using the aircraft of Viking Airlines from Belfast, Bristol, East Midlands, Edinburgh, Glasgow, Gatwick & Manchester. However Viking is currently in administration, so there are doubts as to the future of those flights.
To the best of my knowledge, all of the above operators are 'one class only'. That's unsurprising, as there will be very few business customers travelling between the UK and Crete. For business class travel (or any service with 'perks', such as additional legroom) it would probably be necessary to travel via Athens.
Chris