Each weapon will show a preference for a certain lmaker and/or bullet weight. The only way to know is to shoot all the available ones out there.
100-300 USD
No. Only shoot the caliber printed on the barrel.
.40 cal hollow points. That is what they practice with also.
100-400 USD or so depending on specifics
Depends on finish, exact model, condition. Anywhere from $250-$400.
Most of the federal agencies are using .40 cal hollow points.
Because the gun is old /your using bad ammo /or your just bad with firearm
The Kel Tec in .40 is probably your best best.
Depends on the model, all have their own virtues however the best value listed is the Springfield armory XD .40 S&W.
You would have to define best- what what use.
Sig Sauer P229 chambered in .40 is pretty good
It depends on what you are using it for and which one groups best.