Antibiotics are able to kill a very specific set of bacteria. There are some that kill many different kinds (broad-spectrum antibiotics) and some that only kill a few specific kinds. Frequently, broad-spectrum antibiotics are used if the prescriber doesn't know what the bacteria is or what it is sensitive to. A more specific antibiotic is going to kill the bacteria more rapidly and there is less likelihood that the bacteria will develop resistance to it, usually. So there really isn't a single antibiotic that is better than another in all cases.
Novo-trimel is a sulfonamide antibiotic. This is one of the oldest classes of antibiotics, and I would call it a broad-spectrum antibiotic. Many bacteria have evolved resistance to the majority of sulfonamide drugs.
Baytril is a fluoroquinolone, which is newer but still a broad-spectrum antibiotic. It is frequently given as a catch-all drug for animals when the exact bacterium causing the infection isn't known.
I don't have first-hand knowledge of these antibiotics, and what is best for what type of infection, but I know that the vet can do a culture and sensitivity test if you cannot find an antibiotic that seems to work. In this kind of test, they take urine and attempt to grow the bacteria present in it on a petri dish. They then try to kill the bacteria with several different kinds of antibiotics. This way they will know best which antibiotic is the best one to use. For rabbits, who have a limited number of antibiotics that can be taken orally (penicillins and amoxicillin can be given only as injections), a culture and sensitivity test is a lot more common. I would ask for it the next time you go to the vet. It is possible that novo-trimel will work, and you won't have to go back. If it doesn't work, or you go back because of other problems, ask for a culture and sensitivity test.