Silicon Valley, Israel, Estonia, NYC, LA, Taipei, & Tokyo. Sorry most of Europe, Africa, South America. That said if you can boot strap it and don't need VC work wherever you want.
I believe India is one of the fastest emerging countries taking part in startups. And yeah the USA has a good market in terms of customers but after going digital initial setup doesn't matter but the policies of that country matters the most.
I wouldn't say "the best" but Serbia has some comparative advantages for startups. Personally, I own Price2Spy 2.0 and recently started working on botmenot.com, and in my experience, the biggest advantage here is a very professional and educated workforce (developers, marketing specialists, etc.) for a reasonable salary (much lower than in the USA).
Depend on your product or service. Quite honest internet has already break the rules and this wall of cities or country is been vanished off.It does not mater now a days. Wherever you sit you can grow your startup anywhere in the world.If you sit in USA if your product is not fit it wont work. Even if you based in Israel or even in third world countries does not matter if your product solves problem you will get your pie of success.
The UK has a lot of good schemes for early companies. The US still has to be the best for the network and prozimity to customers alone. I am mostly talking from a tech perspective.
From my side, I don't know why, but I believe that the USA is a good market with a big amount of potential customers, good networking and facilities for comfortable work.
What about you? π