Comparison of Hashing and Modular Exponentiation
Hashing is much cheaper than modular exponentiation, so much so that it is often taken as "free" in efficiency analysis that uses modular arithmetic. My suggestion would be to do a rough comparison, like you said: protocol 1 uses m hashes, protocol 2 uses n exponentiations.

If n>m, protocol 1 is much faster.
If m>a*n, I wouldn't start investigating further until a gets to be around 10^2 or 10^3. It seems unlikely that protocol 1 would use this many, unless if it is using a hash tree or similar data structure requiring lots of hashes.

There is no quick rule because the speed of an exponentiation at this level of scrutiny is dependent on the underlying group. Elliptic curves will be much faster than the integers mod p, and elliptic curve speed will depend on the type of curve.

Similarly, the speed of the hash function depends on how long the input message is. Does it fit into a single block, or does the hash need to iterate over it? 

As one ballpark figure, a 100MHz FPGA can do about 100 ModExps (1024 bit with 160 bit subgroup) in one second, while it can hash about 5000 message blocks (SHA256) in a second.