Each TV in the system reduces the apparent signal strength from the antenna, even when the other sets are turned off. Best bet is to get an amplifier with built in splitter and put as close to the antenna as possible, with each TV getting its own cable from the amplifier/splitter.
This applies to digital TV too, as assuming the signal from the antenna is good to start with, then the boosted signal split between each TV will also be digitally "correct".
Booster/splitters are great for multi TV setups, but are a poor way to fix a poor quality antenna (amplified junk in = amplified junk out)
