1. Other medics. Always top off at 225 if you have 1-2 seconds near them. Hope that they return the favor but keep it moving.
2. Crit-heal teammates. Max heal rate on stock/kritz = 72/s. I'll beam off a fully-healed but not overhealed front line teammate to heal a newly spawned teammate passing by. I might not see said teammate again this life, so keep them overhealed.
3. Front line players. Self-explanatory. Necessary to crossbow front line if you can't keep up overheals via beam. Risky as always but at least 1 medic needs to do this.
4. Snipers. Sniper at 185 survives a quick scope headshot. Do it even if you have half a second of time.
5. Still crossbow targets or clusters of damaged teammates. Just take shots you think you can hit. Only fire a second crossbow if all nearby teammates are overhealed or the shot became easier.
6. Urgent crossbow targets. Near death and you have an 50/50 shot. Sometimes these are across the map and you have to lead the shot to whichever path they seem to be committing to. Urgent crossbows to Medics is implied for #1.
7. Everyone else. Wait your turn.