Easy answer, first class always gets the stat proficiency, starting HP plus Constitution modifier and armor proficiency unless subclass grants the armor proficiency. Depending on what stat proficiency you want with your build should be your first class. If you are lacking a stat proficiency, there is always Resilient feat.
Proficiency
https://bg3.wiki/wiki/ProficiencyHit Points
https://bg3.wiki/wiki/Hit_pointsMulticlassing Guide
https://bg3.wiki/wiki/Guide:Multiclassing_Guide_by_Phantomsplit
