Do you exercise in dim light? I find that in dim light, it can be hard to read those LCD displays. You might want to think about a heart rate monitor with a backlit display. A backlight can really help make it easier to read!

If you are concerned about being able to read the display, you might also want to browse through the heart monitors described as having a "large display". 

I'll feature one product here in particular: the Ekho 351 has a backlight, and the transmitter was voted most comfortable by Prevention Magazine! It is loaded with features, and is even described as "60 lap water resistant".