How about starting with a comparison of available browsers, such as the one from archwiki? This is definitely the most important piece of software.

Besides, I definitely need the following software to even consider a switch from Android to Leste:
* a reliable IMAP mail client
* a reliable XMPP client with OMEMO support
XMPP is my principal way of communicating with family and close friends, which was the top reason why I was unable to switch to SailfishOS and sticked to Android.

Furthermore:
* MStarDict
* some offline OpenStreetMap client, similar to OsmAnd (Maemo didn't really have decent offline vector maps)
* some Anki client

These apps constitute 99% of my daily usage.