E. coli is an enteric bacterium (lives in the intestines) and is one of the primary causes of urinary tract infections (which occur primarily in women).  It is almost always the #1 infecting agent in hospitals and because of that it has become more resistant to standard antibiotics (penicilloins, cephalosporins, co-trimoxazole) ove rthe years.  There is no good answer to your question unless one would have area resistance data.  The CDC website contains good information on resistance patterns and you might be able to determine from the region you live what the "best" compound is to start.  Most clinicians begin with a compound like Cipro (ciprofloxacin) at this point - but agian I caution you that you need to know how the E. coli in your region react prior to recommending.

Daniel A.