Show Recording Dupe Stations

If I have 2 of the same station:

7-1 MyStation hd_720p
7-2 MyStation sd

and I have a show set to record. Will it pick the best quality version of the station or how does that work?

Your Tablo will automatically choose the higher quality station, but you can also ensure this by selecting the 720p channel in the Advanced Recording Options when scheduling the recording.

What if one of the channels becomes unavailable or weak signal? Will it auto use the other?

It won’t if you specify the channel.