Lets face it- this blog has been done before. But hopefully this one interests you.
Both sides are sneaky, literally and metaphorically.The Assassins contact targets through stealth, while the Templars are cunning and secretive. Both groups manipulate and bribe their way through history, such as when Rodrigo Borgia managed become influential in a span of a few short years.
In ACI the two sides were morally ambiguous, with the Assassins being considered the naive brutes by their enemies, while the Templars themselves are dillusioned. In ACII, both sides have been fighting for so long that they've been considerably weakened in some areas. The Templars having been corrupted by their superiors, while the Assassins have lost many of their numbers. The Pieces of Eden are basically driving the two factions insane, and they don't even realize it.By AC:R the Templars in Turkey are more closer to their precursors in Syria during Altairs time, having honor and somewhat peaceful goals. Whether or not this is influenced by the location of the faction is up for debate, with Asia possibly being more true to the original beliefs then Europe. The Assassins in Istanbul are surprisingly advanced, having better equipment and experience then their Roman allies. However, they are notably weaker do to years of being attacked by Ottoman and Byzantine forces.
By ACIII, the Templars have gained an upper hand against the Assassins, which have been reduced to a cranky old guy. They want peace, but Rodrigo Borgias influence still remains. The Assassins have almost no presence in America, but they are more persistent then before and are slowly rebuilding.