I would advise you to swap the engine only if you know how to manage the electricals and other mechanical stuff yourself. If you dont, you'll be at the mercy of the local ustaads and your car would become a sad story. If you currently dont understand the electricals and the mechanical stuff, it would be best to swap in the same engine which would be a bolt on swap and take a year or two to learn about the engine that you might want to swap in the future. Once you believe you can handle most of the things yourself, then only take the plunge.
Coming towards the car. I agree with you, the F6 non turbo is very sluggish and not very good on fuel especially if its an auto. The turbo variant however is a different story. Its very nifty, as I've experienced it in the alto works. The earlier generation k6 isnt very powerful either whereas the later versions are a lot better and its still available in the newer 660 altos. With parts widely available for the HA24 alto / mazda carol / nissan pino, I believe the newer generation K6 with manual transmission would be your best bet. The 'chain wala' as opposed to the 'belt wala' means that the engine uses a timing chain instead of a timing belt which requires much less maintenance.
However, if you were to go completely bonkers, people have also shoved the g15 into the alto, which, if done properly, would be something pretty powerful while being good on fuel, well much better than what you're getting right now from the F6. But that is a swap if you have lots of knowledge about the mechanical stuff especially and the electricals as well and if you have deep pockets because a lot of stuff would need to be upgraded.
