Ch3m1c4L is talking sense, and you should listen to his advice. You gain little in terms of actual working space under the same 1080p resolution on both units. In this case gaining an extra 3'' of physical screen size only affects your dot pitch. Hence you may need to sit further away from the screen than you normally would for a comfortable viewing experience. Add to that various scaling niggles when a lower resolution is blown up, which will be a factor if you visually pick up on these things. Which is why it was suggested you used it primarily as a dedicated multimedia screen, as a kind of cheaper replacement for an LCD TV, for example.
So stick to 24'' at 1080p for all around use at that budget. I would also not discount screens like this Samsung just yet:
http://www.overclockers.co.uk/showproduct.php?prodid=MO-124-SA
Edit: If you are looking for a predominantly gaming screen, you may wish to look at various 120 Hz models on offer at the moment as they will be the most responsive of the bunch for the money.