Definitely think the Philips digital is worth the extra money. I saw it in Costco for £70.
Never had any probs with signal, even at the bottom of the garden and my friend and I can use both our monitors in the same house with no problems.
The parent bit is small and rechargable and the baby unit can use mains or batteries, so I've even put it in the car in the garden when DS had fallen asleep!!
It also has both sensitivity and volume setting, so I can turn the sensitivity down so I don't hear DS 'rustling' but leave the volume up so any other noises, murmurs etc, still come through loud and clear.
ive got Tomy walkabout classic as its in the kitchen plugged into the mains as ive got a big house and im deaf too, so i dont carry it around with me all the time, only now and again if im outside but i can hear it from the kitchen as its loud.. ive had it for 3 months and the batteries only just starting to go down.