For children with high degrees of reflux (4 and 5), in vitro resistance data and hints from recent studies suggest that nitrofurantoin may currently be our best bet for prophylaxis. The micronized formulation (Macrobid) appears to have the fewest gastrointestinal side effects, so I'd use it as a first choice.
If patients don't tolerate nitrofurantoin, we should look at local resistance patterns, or perhaps a first-generation cephalosporin might be the next best choice. It's possible that broader-spectrum antimicrobials may work well in certain patients, but we don't have enough data on the prevalence of mechanisms of resistance, and tendencies to induce resistance, to comfortably use them empirically.
And, of course, we need to remember that when we do decide to prescribe long-term daily antibiotics, we can't assume for a minute that adherence will be complete. As the old saying goes, “Two-thirds of patients take two-thirds of the antibiotic two-thirds of the days prescribed.” One thing for which we have definitive proof is that nobody takes a drug every single day.