In case of wondering I prefer assault squads rather than vanguard. Let me explain this madness.
Vanguard are not cheap, you only get 5 with close combat weapons to start with and they come WITHOUT jump packs. Any additions that you add are just piling on gravy ladelled waaay to thickly. Assault squads are cheaper and do not need many other upgrades (so that will be 1 power fist and 2 flamers in a full squad)
Vanguard are just as squishy as normal assault marines. Yes they hit harder with more attacks but when the return attacks come then they suffer just as easily as regular assault marines.
Vanguard have all these nifty abilities such as heroic intervention but these are hard to get off. If the deep strike goes bad then they are clustered together and could all be taken out by a single battlecannon, To me that would just suck all kinds of bad. Assault marines do not suffer from this as much because they can just be plonked on the table and used as a deterrant to your rhino march.