Hash functions vs Stream Ciphers in terms of Speed
There is a lot of confusion in this question. Hash functions provide collision resistance. However, under a pretty reasonable assumption, they can be used to obtain a PRG or a PRF. Thus, hash functions and stream ciphers can be used to obtain a pseudorandom generator. This is true. (Although RC4 is broken and CANNOT be used for this purpose any more.)

Now, the question is: what is faster? A hash function, a stream cipher, a block cipher, and so on. The answer is very simple! It depends on the function in question and on the platform. If you have an AES-NI instruction set, then this is incredibly fast. It is also a very good option since its security is better studied than any stream cipher that hasn't yet been broken. Hash functions (like the SHA family) are actually pretty slow in comparison. Once Intel puts SHA-2 into hardware, then we'll have to see, but from what I understand it will be slower than AES. If you don't have AES-NI, then things like Salsa20 are a good option. However, my preference is always AES, and unless you really can't use it for some reason, that is always my recommendation.