Search the threads for Ada/Cascade vs. EGR...there have been several discussion on this subject.
Here's my take:
Schools are outstanding in either area.
Demographics are similar in either area (affluent folks predominate).
That's where the similarities end, however.
In the interests of full disclosure, I live in EGR, so my opinions are those of a resident. We moved here 3 years ago, weren't from Grand Rapids at all and had never lived here. We've got 2 kids under 3 and are in our 30s. Sounds like a similar family situation.
Ada/Cascade is suburban living full of newer developments with bigger lots and bigger homes. There are gated communities that are so popular around the rest of the country, there are un-gated suburban sub-divisions and there is everything in between. There are hills, the Grand River (it's gorgeous through Ada/Cascade), the Thornapple River, great parks and an incredible system of bike-paths.
There are plenty of condo developments and I'm assuming some apartment complexes as well though I'm not sure if they'd be family-oriented or retiree-oriented. I'm sure you could find a house to rend in a family-friendly neighborhood. Because the schools are good, people moving to Ada/Cascade are generally families with kids that are either school-age now, or will be eventually. It's also expensive to buy (so is EGR) but if you're looking there you already figured that out.
EGR is a living, breathing Norman Rockwell painting updated for the modern era (take it or leave it). Armies of strollers take the streets every day (I'm only half-kidding...and my wife is among them) to walk around town, walk around Reeds Lake, walk to the library ($9M, brand new in 2006, lake front), walk to the coffee shop, etc. Kids walk to school (there is are no school busses here) and their parents walk with them. There are block parties in the summer, there are sledding parties in the winter. There are candle-lined streets on Christmas Eve (east of Breton Rd. in the Maplewood St. area). Seems like most houses are older, most have garages to the side or behind the house and many homes have that "front porch, hey how ya doing neighbor" thing going on.
That's just how it is.
As you'd expect, with all the walking and front-porch residential, everyone seems to know everyone, at least that was my take when we got here. It was intimidating actually. Now, 3 years later, we're used to it and have our own cadre of jogging-stroller-dog-walking friends. I'd say EGR is what it is....you either love it or hate it and there seems to be no in between.
Property taxes in EGR are considerably higher than Ada/Cascade. That's mainly because EGR is a city and city taxes are always higher than township taxes. Plus, it's a tiny little city that strives to provide big-city type services. Again, if you like that, you'll feel it's worth the money. If you're moving from a township where you pay low taxes, EGR will be a shock to the system.
Because the taxes are high it seems that the only people buying homes are families with kids, families with babies, or couples about to have kids. I mentioned that about Ada/Cascade too, but I think it's to a much higher degree in EGR. I haven't seen a house sell in the 3 years we've been here where the new buyers weren't parents w/kids save for one couple on our street who is adopting next year.
From a rental perspective there are a few duplexes around downtown EGR ("Gaslight Village") but other than that, renting here means renting a home. To find those, try this link (works for Ada/Cascade too) and search by school district (for Ada/Cascade search "Forest Hills" school district for EGR search the EGR school district which is almost the same as the city-limits save for a little extra chunk of land that's in GR Township + EGR Schools)
http://public.grar.com/public/pubsrch.mac/start
Send me a private message if you need any more details.

Either place is nice, good luck in your search.