I tend to prefer the 49 key controllers. Personally, I use a lot of octaves in my work - often the same note differentiated between octaves, so a smaller controller is limited in that regard when playing 'live' in. I tend not to quantise anyway, so I don't have the need to re-work parts once they're played. Hence I used a 49 key controller and leave the tracks without adding in the extra notes in the different octaves later.
However, the footprint of a 49 key controller is significant, so if you want to save space, get a 25 key one.