I'm looking to purchase an outdoor and indoor hotspot. Which are the recommended antennas for both (Indoor/outdoor) for better coverage.
The answer is: "It depends"
First you need to know what the difference in Antenna's are. You can think of it as a speaker phone putting out noise. The speaker with the longer narrower cone projects further but much narrower, so you can't hear as well above and blow that cone, but directly further out you can hear much further away.
The hotspot and whichever antenna you pick will output the same amount of RF power. The difference in the antenna gain (3dBi/5.8dBi/8dBi) will give you narrower more focused signals.
This article by Nik is a really well written in depth post on configuring your hotspot for the best coverage possible: http://kyk13.com/life/a-rough-guide-to-helium-hotspot-placement/