The ideal solution?
Putin and Kiev get at the table and agree to let an international troop on Crimea, replacing the Russian soldiers which retreat back to their barracks on their naval base. Under surveillance of this international troops, a genuine, free referendum is held about the future of Crimea, and both Russia and Kiev agree to respect it.
Yeah... like that's gonna happen.
I am really confused what the OP meant by "best" too. Best for whom? And is the "best" even possible?
Best for Crimea? well even without the russian meddling into Crimea, most crimeans, at least 60%, don't want to stay with Ukraine. I don't know how that translates into wanting to be with Russia, but it certainly means that if they want to be independent from Ukraine, by the rights of self-determination established in Europe in the 1800, they have that right.
But is that best for Ukraine? I don't know...
So "best" is a pretty juvenile way to look at things.
But you proposed the ideal situation, I'll propose a realistic one.
Crimea will vote for independence from Ukraine and become, in some manner, part of the Russian Federation. Either fully part of it, or just a modern version of a vassal state.
Ukraine will cut it's losses and try and keep eastern Ukraine under control and not let another "crimea" happen there.
Some nations will recognize Crimea in the new capacity, some won't. A sort of a Kosovo situation but with a much larger and scarier "Serbia".
The EU will bailout, maybe twice, Ukraine, and swiftly begin ascension program so that Ukraine will be "out of the reach" of russian influences. Moldavia may also be put on the fast track there (expect problems here too). By this time next year, we'll have an EU army, a real one and at new drone programs for R&D. Also, all the countries will start paying more attention to renewable energies and start increasing liquid gas imports from the USA and brazil to offset the reduction in natural gas from Russia.
This whole Crimea thing has until the end of the month to explode. Soon there's a national referendum of the people, not the BS decision that lawmakers in the regional parliament of Crimea made. And that referendum will vindicate the decision for independence and at that point, we'll be in clear. Ukraine will shut it's mouth and accept that because it has no choice... and evacuate it's forces from Crimea and this whole very tense situation will be a bit less tense. But until then, there are 1000 different ways this can go wrong.