What are the best medical alert companies? Dad is 90 and walks everyday. I need one that works away from the apartment.

I used one provided by a local alarm service.  It's been in business for decades.

Before making a selection, I contacted half a dozen or so companies, including the ones that advertise regularly.    If they wouldn't connect me to someone who could answer questions but only wanted to send information, I dropped them immediately.   Brochures are just full of advertising material; I had questions and wanted answers.

Another potential one took 2 - 3 days (don't remember now) to return my phone call.

The company I settled on was a well known system alarm company, and the choice was a good one.   They responded even when Dad just bent over; they followed up, calling repeatedly if he didn't respond.  

I plan to get a pendant for them when I think I'm ready for that level of monitoring.  After the research I did, I wouldn't even bother with the ones that advertise heavily.

I got Medical Guardian for my grandfather. I saw it first suggested on this site, and it had good reviews when I researched.

I'm going to suggest you do a web search for "gps medical alert systems", I've come up with several sites offering up to date comparisons.