My 12" PB 1.33 GHz 1.25 GB RAM didn't run Leopard too well. It took forever to start up and it couldn't multitask very well. Leopard boot-up time was about 1:30 minutes. I put Tiger back on the laptop and it boots up in roughly 39 seconds. My G5 PowerMac boots up in leopard in around 35-40 seconds depending on the temperature in the room.
Leopard will allow you to put on slightly more modern software, but Tiger is in my opinion more stable than Leopard. Just weigh your pros and cons with both Tiger and Leopard, give each pro a positive value between 1-10, each con a negative value between 0- (-10) and add them up. Whichever OS has the most points is the choice you should go with.