there aint much in it if you stick to respected remappers on here which include:
revo
custom code
APR
Jabba
P-Torque
AMD
Forge
Ive tried to put them in order of popularity, (most pop first) but this is not to say this is order of how good they are.
For example, Forge are a very respected company and im sure do a fantastic job, but did come to the party later than others and people do tend to follow others. Also some offer national coverage and others are only in house and so tend to be limited by location.
As said above, stick to this list and do some reading on this forum and you cant go wrong.