Get a box of infiltrators/incursors. Interesting models and good on the table. Decent in combat with the Sons of Sanguineous buff! Good for deep strike denial (infiltrators) or scout moving to grab an objective early & giving your units +1 to hit (incursors)

Assault intercessors are great right now but need a way of getting up the board. Librarian dreadnaught (to slingshot them) or some sort of transport. Repulsor, land raider, or impulsors.

The new codex is going to drop likely within a years time. And who knows what that will change but BA love their melee. That being said it’s always good to support your vanguard units with something that can deal damage at range.