FWIW, I wouldn't recommend using the number of shares as the benchmark for comparing offers (across any two companies, startups or otherwise).

Actual share counts are quite arbitrary. It's common for startups that are going public to do a 10 to 1 stock split shortly beforehand. Using your algorithm, an offer from that company would 10x more valuable the day after the split!

Much better would be to compare the expected value, by multiplying the ownership percentage by some estimate of the value of the company.