LCD is a liquid crystal display (LED is the light source used), while plasma uses a gas-and-glass technology.
Both are great panels, but each have strengths. Plasma will generally be less expensive "per inch" when compared with LCD or LED, but LED will be less expensive to run for power consumption.
There are a lot of benefits for each of them, and a Best Buy salesperson would probably be able to assist you better in helping you choose one for your personal and particular needs. Before making any decisions, it's also a great idea to go and check them in person to see which picture best appeals to you.
Thanks for your interest in Samsung products.
--Mr. Samsung