Hey, can anyone tell me the difference between these 3 types of masters? I'm set to do a 12month MRes...as its longer than most MSci's, is it valued higher?

An MRes is a training in research and research methodologies. It is ideal if you wish to move on to a PhD. If you want to work in research or go on to do a PhD it will probably be of more use to you than an MSc with a lesser research component. However an MSc in one university may provide a very similar training (and go on as long) as an MRes in another university. These titles, although a strong indication of the aims of the course, are really a question of branding.

The MPhil is distinct. It is a degree by research. Most universities require PhD students to register for an MPhil, before changing their registration after 12-18 months to that of PhD. It is unusual for students to start an MPhil with the intention of completing it - most intend to transfer to a PhD. This process allows universities to weed out students who they feel may not be up to completing a PhD, without upsetting their PhD drop-out or failure rates (ie the candidate hasn't failed a PhD they have passed an MPhil). Conversely it allows students who run out of motivation or cash to write up an MPhil thesis, rather than carry on for another 2 years. MPhil's are also sometimes awarded by PhD examiners who feel that even after three or four years research the student has failed to reach the standards required for a PhD.