Question
is miracle better than cow manure for tomatoes.

Answer
I would avoid Miracle Gro completely.  Cow Manure is the better choice, but not for growing Tomatoes.

Un-cured Cow Manure commonly harbors E. coli and other pathogenic protozoa, viruses and bacteria (remember the Salad Scare 2 summers ago?).  Cattle Manure is held to be a 'primary reservoir' for E. coli 0157 -- as high as 50,000 cfu/gram of Manure; people get sick on only 10 cfu.

Manure is rich in Nitrogen, Potash and Phosphate.  Over-use, however, will trigger the same problems as over-use of any Chemical fertilizer.  Use of Chicken Manure from chicken farms in some regions has created a pollution problem and a buildup of Phosphates and Potash in farm Soil, causing shortages of other minerals.

Ongoing use of any Manure will lower the pH of the Soil, causing a host of other problems.

Plus you eventually find a buildup of Salts, just like you would with Miracle Gro.

Compost and Humus contain oodles of Organic Matter without the risk of pathogens and other things that come with Manure.  All are far superior to chemical fertilizers, which do more harm than good.  No matter what pictures they show you in their ads.

Any followsup please let me know.