Vilnius for a weekend, or the loop out to Nida
A long weekend in Vilnius with a day out to Trakai Castle is the trip the 3 GB pack was made for: maps, tickets, messages and a few photos, with 15 days of validity if you stay on. Most first visits run longer than that. A typical week to ten days goes from Vilnius to Kaunas, then west to Klaipėda and across to the Curonian Spit for Nida, often with a stop at the Hill of Crosses near Šiauliai. That is a lot of navigation and timetables on the move, and the 5 GB pack, valid for 30 days, covers it without you keeping count.
If you are in Lithuania for a month, visiting family or working from Vilnius, the 10 GB pack fits a normal routine, and the 20 GB one leaves room to share the connection with a laptop, since hotspot is included. The data calculator works it out from your own habits.