Drupal 7 and google maps v3. Which is the module to use ?
The approach should be map agnostic. You need to break things in two parts:


Storing location data
Displaying this data on a map


1) Data storage. 

You'll need three modules here:


Address field to store addresses (http://drupal.org/project/addressfield)
Geofield to store latitude/longitude (http://drupal.org/project/geofield)
Geocoder to geocode addresses from addressfield into lat/lon for geofield (http://drupal.org/project/geocoder)


It may look difficult, but it is really easy to configure these three modules to play nicely.

2) Data display. 

Now having data stored in database we can choose any display approach we want. Here you have two+ choices:
  - GMap (http://drupal.org/project/gmap)
  - OpenLayers (http://drupal.org/project/openlayers)
  - As a third option, you can have a custom js code which plays with Google Maps

Everything depends on your final goal. OpenLayes plays with different map engines and to me it looks a bit bloated. If you go with GMap you'll get Google Maps V3 support which is better to stick with instead of Google Maps API V2. Google Maps API V2 development has stopped, no new features are being rolled and it can be abandoned at any moment, so why to risk?

Go with custom js maps code if GMap module doesn't give you what you need. But I do really suggest you to look at GMap module a little bit closer.