Wow, thats a loaded question!!! I usually suggest reading a book or two regarding snakes in general to get a feel on the different species readily available in the pet trade, their eventual size obtained, general demeanor, and any specialized care requirements they may have. Same with lizards. Basically, it all boils down to how much time, space, and money you are willing to invest in your new pets. From a space and money perspective, most corns and kings offered are excellent choices as they have good temperaments in general, most won't outgrow something the size of a 20-gallon long aquarium, and most can be kept close to room temps (75-85 degrees) and dont require costly heating systems if a warm spot is needed based on your house temps. The plus is also in feeding them. Most only require mice of various sizes for food. If you have more space, you could go with something in the boid family. Ball pythons and colombian boas are generally known for good temperaments. However, they require larger (more costly) cages and also feed on larger (more costly)food items like small to large rats. Also, a large female colombian boa can EASILY get over 8 feet long and require jumbo rats as food and a LARGE cage to house in. The boids also require higher temps and are less forgiving if kept at lower temps. They will definitely need a warm spot in the cage between 85-90 degrees, so a more expensive heating system may be needed.
Same with lizards. A leopard gecko will be small and skittish as a baby, but will mature into a fairly calm, decent sized lizard. The plus on the leopard geckos is they can be kept in a 10-gallon tank, and can be heated fairly easily. They do not require special UVB lighting either. On the other hand, bearded dragons are great pets, but require larger cages, heat, and UVB lighting.
There are tons of options based on what you are looking for as a pet. Do some research, get on line, and go to local herp shows to see whats available and what their care requirements are. You need to look at the long term cost of keeping these pets healthy. Reptile housing, feeding, and heating is not as no-brainer as keeping something like a hamster, so do your homework!!
KevinM