If my ultimate goal is a PhD in the US, is it better to do an unfunded MS in the US or funded MS at the IIT/IISc?

As i see that you have safe universities with rank of from 50 to 60. So i would suggest go for M.Tech. in IIT/IISc depending upon area in which you want to pursue research(not MS in India). Why am i saying this because there is a flood of PhD scholars in US. So to separate yourself from them you have to get in top 25 colleges in US. It is not that lower ranked colleges doesn't matter but in the end college matters alumni, faculty, research facility all of this needs to be there. I am not suggesting MS because for PhD you will get funding, but for MS there is 98% chance you won't get. If you take loan for MS then you won't be able to pay it back because during PhD stipend is not that high. You can improve your profile during M.Tech by publishing some papers. I hope my answer helps you in making your decision.

First of all, congrats on your self-developed interests. Theoretical computer science is a wonderful topic and it's neat that you've discovered it for yourself. Each area of CS has some required coursework, but can also make do with some things formally missing. For instance, many theory professors will not care much that you don't have a lot of systems coursework. But, if you can't demonstrate somehow your competence in and aptitude for theory itself, it'll be hard to get admitted for a PhD. I don't know that a US master's is your best choice. You'll have to pay for it at most (good) places, and the amount of research you get done is somewhat limited (depends on the place, professors, etc.). In contrast, it sounds like you can get a good research master's in India. If that's so, you may be better off going the latter route. A master's from a good Indian university, with quality research, will not count against you at all. In short, I think you've read the situation absolutely correctly. At Brown, we have seen, admitted, and enrolled students in similar positions, whose undergrad was not in CS but who switched to CS in the course of their master's (including situations very similar to yours, where the student did a master's at IIT to switch to CS). We're certainly very open to such students, and I expect so is any other place. Especially if your statement makes clear why you took that particular path. Nobody would be surprised that you chose to stay in India to do a funded master's than coming to the US and paying for one!

has already given a better answer than I would have given you. Let me add one more thing about finances: Unless your parents are super-rich, it would be very hard for you to live a comfortable life (with Rs. 65 to $ 1 and increasing ratio). I have seen many unfunded Indian masters students who live in very poor conditions because of financial constraints. If you don't have proper living conditions it would be very hard to concentrate on studies. You can do it but it will be harder. If you take loans, there will be constant pressure of paying that off. IIT/IISc will give you much more freedom to do what you want. There are good professors in these institutions who can help you build your research profile. Since the funding is not tied to a particular professor, you could choose to work in an area you want. There will be no tension of loans or unnecessary worry of buying a Rs. 800 buffet at Indian restaurant. My personal recommendation would be: Do your M.Tech. from India and start working on your project from the first semester. In that way you would have about 1.5 years of project work to show for in your Ph.D. application. Good luck. PS: I am a conservative guy. I would have never gone for a Ph.D. to US if I had not gotten full funding.

It is time you do your first lesson in managing Finance. You have two options here, (i) MS from India and PhD from US --> Both will require almost no initial investment and no money during your course, as you get stipend. So, its zero down and zero payment for you! (ii) MS from US and PhD from US --> MS from US can get very costly and may require you to work a 2-4 years in US, just to pay your loans. So, there is a lot of investment required here upfront with a possibility of extra 2-4 years depending upon whether you take a job or not.Now, you have one more dimension to consider. I am not saying that you choose MS from India straightaway, but it does gives you somewhat better understanding and you can make your decision more judiciously.Keep in mind that the prerequisites for MS in India and MS from US are very different. Getting into IISc can be very difficult based on GATE exam. And if you don't have great references/publications then getting into a good US university is also very difficult.Weight your preferences, abilities, responsibilities and finances and then take your call.

Also after pursuing your MS, it might be worthwhile to gain some industrial exposure for like 2-3 years before taking up a PhD. This experience will encourage and equip you to conduct research that is relevant to the industry and will make you aware of how things work in the corporate world.

Start MS in US ( select research and thesis based MS program ) and try to convert that further into funded PhD .. Like this you can finish MS and PhD in 4-5 years.It is possible to do this. Just make a road plan to achieve the target.