People ask this all the time, but really it's "best" in terms of what? I have a hard time thinking of anything that makes a bass better for beginners than for pros other than the fact that beginners might not want to spend as much money for a particular tone. It's like learning to drive -- you can learn how to drive in a used Chevy or a new Mercedes, both have a steering wheel, gas and brakes. In a bass, you want four strings and pickups that work. Beyond that, it's what you want to spend. If you want to spend $2000, there's no reason you can't learn on a Rickenbacker or a Stingray or whatever. If you want to spend $200, learn on an SX or a Squier.