If you just use A-Z, a-z, 0-9, you have a password space containing a little over 95 bits of entropy (log2(62^16)). A randomly chosen password should be reason

If you just use A-Z, a-z, 0-9, you have a password space containing a little over 95 bits of entropy (log2(62^16)). A randomly chosen password should be reasonably secure against most attacks.