I'm also considering which one to buy.
For me it's important to have a google maps on my blog that can locate me with an update once of twice a day. Even if it's not google maps but I want people that will read my blog to be able to follow me.
Do any of the two devices allow this?
SPOT allows for a share page - not sure if you can embed the actual page - but you can setup a map page that you can link to. You can also tweet and FB updates out (I don't).
And I just saw they have 3rd party forwarding - it looks like you can forward your coordinates to a 3rd party GPS / mapping site... so that may work well for what you want to do.