Which of the following will give a better quality of voice and overall better skill in music- Learning Indian Classical music (probably on a western Instrument like harmonium whose frequencies are different) or singing by 'voice trainers'?
Long story short: if you live in an area with strong Indian culture and are very familiar with Indian Classical music, start there. If you just think Indian music is cool, start somewhere else.
Either one is going to provide you with a lot of the fundamentals of vocal training (breath support, pitch, posture, etc.) Anything that doesn't overlap between the two (specific techniques, repertoire, community, etc.) will have very little crossover (unless you learn both and create a crossover yourself). Here are a few things to consider:
1. Location and local culture: If you live in an area where Indian Classical music is prevalent and it is more familiar to you it may be a good place to start (especially if you are not familiar with western vocal music). If you live in an area where Indian Classical isn't common and you are not already familiar with it (like, adolescent nostalgia familiar) and you just think it is cool, don't start with it (you can always pick it up later)
2. Resources: How difficult will it be for you to find educational books, teachers/tutors/mentors and decent repertoire? This is closely related to #1, but goes a step further. You may have grown up with Indian Classical, but if the only resources available to you teach western vocal technique, this is something to take into account.
3. Personal preference: Are you particularly passionate about one or the other? Don't skip out on what you enjoy because you think the other will be more beneficial. If you have the resources available to you (as described above) neither will give you a significant advantage over the other in terms of vocal training.
Finally, my personal recommendation: learn both. It's always a good idea to diversify, there are likely techniques from one that will at least teach you something about the other and most of the things you learn will apply to both anyway. Wherever you are, there are likely plenty resources for at least one of them and thanks to the interwebs I'm sure you could dig up a fair amount about the other.