GeoAPI
+ Got us an API key within 5 minutes of requesting it
+ Comes with a comprehensive list of points of interest, from place data (restaurants, bars, ...) to other (parks, cities, etc...) for the US. This was the single most important factor as it enabled us to build a place-aware application without worrying about places too much
+ Has an API that scales and easily handled our bump in traffic due to being TechCrunched
+ Has extremely supportive and fast technical support and issue resolution. The engineers, despite being at Twitter, still react in "startup-time" which is critical to our success
SimpleGeo
- Took 2 months to get us an API key
- Still has no POI data. This is apparently coming in their marketplace but will cost an extra fee and there's no way to test the quality of the data to-date
Basically, it was no contest. I have no doubts that the SimpleGeo guys have built a great way to index & search for data spacially, but without a comprehensive POI database, the effort required to build a geo app is much greater. With GeoAPI, we not only got fast geospatial search but also a well organized list of POI to go with it.
Hope this helps.