Lets to sort through the various motivations why the Allspark is sought.

Megatron: He wants to build an army with the Allspark.

Optimus and Sentinel: They wanted the Allspark to restore Cybertron.

The Fallen: Primarily use the Allspark to find the Matrix in order to kill humanity out of petty revenge. Oh build an army to spread destruction in the universe.

Megatron and Sentinel Prime: The compromise and truce meeting on Earth where the Allspark is. Megatron gets to build his army. Cybertron gets restored satisfying Sentinel.

Optimus: He would rather have the Allspark destroyed rather than the Decepticons have it to conquer or destroy other sentient beings like Humans.

 

Again, Redwolf, your logic is undeniable.

 

One thing they have in common: They all wanted to rebuild Cybertron.

Differences are:

Megatron - Build an army, comit genocide upon the Autobots and rule Cybertron like a tyrant [and possibly the rest of the Universe].
Wipe out mankind is a bonus.

The Fallen - Same thing as Megatron, but on his case, definetely conquer the Universe and definetely wipe out mankind, he really hates us more than anyone else.

Sentinel - Working alongside Megatron [thus going along Megatron's objectives], but making his own changes on Megatron's plot:
- Autobots who surrender would be spared.
- Megatron's tyrannity would be kept low.

Optimus - Rebuild Cybertron only, but prefers to die over letting the Decepticons have it.
He also seems to be fairly certain that the AllSpark must be destroyed to stop the War, so he would likely destroy the AllSpark after rebuilding Cybertron [or hiding it].

 

Interesting