Yeah, Lithuania can survive- often the USSR-Germany border ends up with Lithuania being trapped between the two. But as to how you're supposed to make it a superpower... beats me, I'm afraid.
In South America, I'd say that Brazil can be considered the weakest, simply because it's got such a huge area to defend and if you can't secure the coast you're screwed.
Peru and Chile are surprisingly good- no-one can ever be bothered to attack from the coast and both are quite mountainous. Peru is a favourite of mine- if you can take over Bolivia and Ecuador to gain more IC without the US DoWing you, you can easily attack Brazil through the Amazon Rainforest.
In Europe, I'd say Romania and Turkey are surprisingly good. Turkey can actually defeat all the Soviet divisions in the Caucasus if you try hard- there are surprisingly few there. The problem with making a Turkish empire is that you can get far down to Jerusalem, but then the Brits send over all their troops from Egypt. If Turkey wants a Middle Eastern Empire, you'll have to wait until the Italians attack Egypt.
Afghanistan is also alright. Unlike Persia it doesn't have any alliegances or obligations to the UK or USSR. Mountains of Afghanistan allow good defence and if you can build a few cavalry divisions and time the attack right (usually if the Germans get Moscow), Central Asia is yours.