Plano is a combination of new and old - it is spread out somewhat with pockets of "good" and "bad". There is new construction, but a big portion of the houses are older (not old - I mean like 10-20 years).
Coppell is predominantly new construction - houses are 1-5 years old.
Why does this matter?? Well, usually, in most cities, the best childcare, schooling, etc. pops up with new construction. New construction, too, usually means younger families with younger children. So my advice is to pick an area of new ocnstruction (even if you don't buy a new house) - this is aplenty in Coppell, takes some searching in Plano.
Not sure job-wise where work will be located, but the traffic situation in Dallas can be a nightmare and it is definitely worth your while to investigate this angle. And if traffic not a big deal, you might consider Frisco - it's a relatively "new" city just north of Plano that has mainly new construction, great shopping, etc.
To arm you with more information, I'd also check out the school districts - look at statistics, etc. These two cities are in different school districts. A good website to look at is www.localschooldirectory.com. From here, you can pick a city, then particular schools, etc - and it has links to the school district websites.
Good luck with your search, and welcome to Dallas!