+1, though it does depend on your style of play and the list you are using.
The more competitive style of 'vanilla' Marine list contains 2 Warhounds to provide solid AT capabilities and to act as the link with the main forces, 1-3 Thunderhawks and 1-2 Terminators to provide mobility and assault capabilities and usually 1-2 ThunderBolts to provide air capabilities as well as boosting activations - to a total of 6-7 activations.
The remaining 4-5 activations are usually infantry of one kind or another rather than AV because they provide more specialist capabilities that the player wants to exploit (firepower, assault, scouting etc)
Land Raiders, Predators and Whirlwinds tend to be less usefull because they are more static (Whirlwinds), or the Warhounds are considered better and cheaper alternatives (Predators and Land Raiders), which is why there has been significant debate on how to improve the balance of these formations. That said, along with Dreadnoughts, each has their place and there are many players who would choose to include one or more of these formations for particular roles.
For example, I really like to use a Landing Craft carrying Terminators with Dreadnoughts and Chaplain upgrades to deliver the best air assault for its cost (850 points for 7x MW and 10x normal dice, most of which are 3+). However, this assault does shape the rest of the list which has to be geared to exploit the results.
However, it is also vulnerable to AA, and a critical hit can occur on the way in, which can really ruin carefully laid plans
(which is perhaps why this is not considered part of the optimal list 
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