A digital heart rate monitor greatly reduces the problem faced by analogue heart rate monitors: interference. Most heart rate monitors these days however use wireless analogue transmission technology to communicate between the chest strap and the wrist watch. Only a few use digital technology. There is a small downside to digital chest strap: it cannot interface with gym equipment, so you will need to bring the wrist watch with you if you exercise in a gym. For most people this is hardly an issue.
Below is a compiled list of digital heart rate monitors that have been featured on this web site. It is not an exhaustive list.
Note: The Oregon Scientific SE211, SE212, SE232, SE233 all have switchable transmission i.e. they can switch between analogue and digital transmission at the touch of a button.
The preliminary list above can be narrowed down further to include the more popular and/or well-regarded ones for each of the following categories.
This shortened list is merely intended to provide the starting point of your investigation, especially if you are short of time. You should not rule out other monitors not on this list as they may well have other features that you will find very useful. For example the Oregon SE211/212/232/233 series have switchable transmission - a very original and unusual feature which you may want to investigate further.
The most advanced ditigal HRM featured on this web site is the Polar RS800/RS800SD system intended for professional runners and athletes. It is highly complex and if you are a general fitness exerciser, you will find other choices more suitable.