Definitely go for a burm over a retic as a first giant. Burms have SUPER AWESOME temperaments on average, while retics can sometimes be nasty. A male burm will grow to 10-15' long and up to 100lbs or so.

A burm will never refuse a meal on you (unless you're doing something wrong) and are really great snakes. An adult male will need a nice 8' cage or a 10' as an adult.