I'm going to explain why Assault Marines and Vanguard kinda suck for Codex Marines. This is only in reference to Codex Marines and does not include Blood Angels, or Assault Marines in any other army.
Firstly, the normal Space Marine Codex is primarily good at making shooting armies. About the only truly awesome assault unit in the Codex is Assault Terminators. Other than that, you just get a lot of average. Thus, most people that want to have an assault element in their Codex Marine army will take the most potent assault unit available (i.e. not Assault Marines).
Secondly, Assault Squads use Fast Attack choices. Fast Attack slots are usually better used on Land Speeders or Attack Bikes because both of these units bring extremely mobile melta weaponry to the table which is something that most armies require nowadays to have any realistic chance of cracking tough armored targets.
Third, Assault Squads aren't cheap. A minimum sized unit is basically useless because no matter how many upgrades you give them, 5 Space Marines on their own just aren't that tough and they will die, probably pretty quickly too. A larger squad is more resilient, but then suffers from costing more points and still only being decent at close combat. Assault Squads are better than Tactical Marines at close combat but give up the ability to get a heavy weapon, don't have bolters, can't take melta weapons (which are pretty much the best special weapon available) and have a habit of falling back entirely too far when using Combat Tactics because of their jump packs.
Vanguard take all of the problems that Assault Squads have and magnify them. If you want them to have jump packs they start getting expensive and that's before increasing the squad size or giving them any sort of close combat upgrades. Even if you go nuts and buy everybody a power weapon or something, they're still not as potent an assault unit as a squad of Terminators and aren't half as resilient due to their inferior armor save. Vanguard also eat up a Fast Attack slot just like normal Assault Marines and manage to cost even more points while doing it. Vanguard have no access to decent ranged weapon upgrades unless you have some strange requirement for a unit with a ton of plasma pistols in which case I suppose they could be useful for that.
All in all, if you want an army that uses a lot of models with jump packs use the Blood Angel Codex. Codex: Space Marines is not designed for this and your army will suffer as a result. If you're just looking to include a single unit of jump packers in your army, be absolutely certain that you don't require the Fast Attack slot and that you have all of your other bases covered before spending points on Assault Squads.
Hope this helps.
