I have a lot of experience with freshwater snails
MHO the two best kinds of snails to have in your tank are Malaysian trumpet snails (MTS) and the Pomacea bridgesii.
MTS are small and look liek unicorn horns. they don't breed quite as fast as other small pest snails. the live in your gravel and come out mostly at night and clean up. they stir up the gravel in the process. stay away from the other pond snails they breed faster and will out compete the MTS and aren't as usefull to the tank and arent as pretty.
When I kept freshwater tansk I woudl keep several MTS snails IN the power filter they woudl crawl along the mechanical filter and eat all the bits of un eaten food and other nastyness. I also got lots of small fresh water mussles and put them in a filter cartridge to help naturaly filter out fish and snail waste from the tank. this doesn't work very well in fresh water, but clams and mussles ina slate waater filter work well.
Pomacea bridgesii is the best kind of apple snail to get. DON'T TRUST THE PET STORES TO IDENTIFY THE SPECIES THEY ARE FREQUENTLY WRONG. Bridesii snails are great because they ONLY eat dead and decaying matter. if a fish dies in your tank they will eat it quickly. I think every freshwater tank without agressive species should have 1 for every 5-10 gallns to eat any dead fish fast before they polute the water. the other species comonly found is the Pomacea canaliculata. it grows larger and will eat living pants. Because it will eat living plans it is more likely to eat algea than the bridgesii, but the MTS will. if you go with a cana you can put water cress in your tank and it will grow like macro algae woudl in a fuge and the cana will eat the watercress as a food source.
This website helps you identify the snails
http://www.applesnail.net/content/species_genera.htm
The entire site is AMAZING.
the other thing to know about apple snals is they don't fully digest their food. there excrement makes great fry food and also the MTS and pest sanils may eat the refuse. don't over feed them because they will polute the tank. on the other hand don't treat apple snails liek a clean up crew. they need food, they need calcium too. hikari makes a GREAT food called crab cuisine. also put some calcium sand or crushed oyster shells in the tank (or better yet the filter) to help buffer the calcium.
apple snails do not need to be transported in water. they have a lung and a gil. They can be transported ina damp paper towel so long as they are not exposed to extreme temperatures they can stay there for months. this means if you have any sort of problem with them in your tank you can quarentine them on land. also if you transport them out of a bag of water you don't need to aclimate them as you woudl a fish.
inverts in freshwater aquariums are also great as a canary in a coal mine. they are the first ones to be adversely effected by poor water conditions.