It's a bit of a difficult question to answer really, because it really depends on exactly what bacteria there are, where they are, and what they are resistant to. The only real way to tell is to get a culture and sensitivity test done (before antibiotics are started otherwise the results will be affected) although they do have an annoying habit of sometimes coming back with nothing having grown. I still think it's worth doing up front though as if it's likely to be a recurrent problem (and if this is the second time it has flared, it may well be), you can spend literally months or years faffing about with different antibiotics trying to work out something suitable.
My vet usually goes for engemycin/terramycin LA as a first choice, as it is broad spectrum and is one injection every 3 days so it's pretty low stress to give if you can inject. Others include septrin (inactivated by pus so not a good choice for very pussy snuffles), penicillin (injected only) especially if it might be a tooth root abscess, and/or metronidazole if the infection is tooth root related. Metranidazole is what seems to work best for my little snuffly angel, hers is tooth root related - but it does not kill pasteurella, which is why it's important to try and get a sample taken first. Depending on where it is, your vet may be able to do a conscious or sedated tear duct flush and get a sample from the nose from the flushed liquid, or a deep nasal swab can be taken but the bun will probably need to be fully sedated for that. Many vets now also think that a long course (maybe 6 weeks or more) is necessary to kill off all the deep-seated bacteria without just letting those more resistant to the antibiotic to flourish.
I do think it's important that you really treat these aggressively as they can become chronic very, very easily - more effort up front could well save you years of ongoing hassle!