There is no "better" or "worse" with these zip codes. They both share the same school district and, geographically, are pretty much the same.
Elm Grove (53122), is a mostly non-business community. They have no major businesses to support their tax base, so property taxes there can run a little higher than Brookfield (53045 and 53005). Elm Grove has a little more of an "exclusive" air to it and some of the houses there reflect that. They run the gamut from modest homes built in the 50's to large mansions built in the last couple years. Most of the older homes have very unique architecture and unusual floor plans. Also, being more land-locked, Elm Grove homes generally will command a higher price-tag than the more expandable Brookfield area.
Brookfield also runs from much older houses to brand new models but the architecture and layouts tend to be more tradition with a few exceptions.
Overall, your kids would go into the same school system, you'd shop at the same stores and have the same commute regardless of with zip code you choose. About the only major infrastructure difference between Elm Grove and Brookfield is that Elm Grove is served by a community well while the vast majority of Brookfield is on a municiple water system with some exceptions of private wells.
I hope that helps.