First of all, I think there is no such thing as a perfect form of government... All systems have their pros and cons.
As for what the best form of government is, I don't really know. However, I would choose the constitutional monarchy, provided that it is a representative democracy of course.
It means that the head of state can be a constant in a country where changes in political relations may frequently occur. You won't up losing a head of state (who is often also the political leader) that is finally getting some experience and getting some rookie in return.
It also has the added benefits of not having to spend millions on presidential elections, nepotism and redecorating presidential residences (let's not forget that bit!
).
And of course, elections shouldn't be based on a district system, as this would inevitably lead to misrepresentation.
Quick example for an election with two parties (A and B) and districts with equal numbers of voters:
A wins 51% of the districts with a 55% majority
B wins 49% of the districts with a 60% majority
Party A has 47.65% of the votes, but gets 51% of the representatives
Party B has 52.35% of the votes, but gets only 49% of the representatives
Now over 3% of the population isn't represented and those who voted party A are overrepresented. More importantly, due to this misrepresentation new government policy will now be made to suit the wishes of the minority...