Vistara has terrible availability and very few routes to Europe and all mostly from Delhi, you'll be charged the leg from wherever in India to Delhi. Also you'll restrict yourself to the very few flights they have weekly and you might not be able to get your whole family in the same plane.
Just for quick comparison
BLR-FRA Economy One Way - Early December
United 36k + 3200 INR (would cost the same miles from Delhi than a lot of T2 cities in India, for example I could fly from Pune or Goa and it would cost the same)
Vistara 37.5k + 3500 INR (or 30k if depart directly from Delhi + 1500 INR)
Turkish 30k + 10000 INR (not available from BLR so I replaced with Delhi not sure if they charge more miles in case of additional leg on itinerary also surcharge definitely higher, if partner airline expect over 15000 INR in surcharges)
Qatar 32.5k + 1600 INR
Singapore 30.5k + 1500 INR
So you'll need to do your research in each case and your specific route you want. Vistara doesn't fly to most of Europe and flying regionally in another airline with a family might rack up lots of charges in baggage fees very very fast.
By right both Turkish, Singapore and United will let you book on Vistara, Air India, LOT, scandinavian, eurowings, cityjet, air lingus, Lufthansa and a lot more. But another thing is in real life, try booking Vistara flights via Turkish Airlines. Routing restrictions are an issue and so are surcharges in Turkish but the required miles are less (so in the example above paying 6k miles less is worth paying 7k INR more in fees and having a stop in IST?).
Also awards on partner airlines will most likely require you to call Turkish Airlines and not sure if they charge an additional fee for that.
Be mindful as well you can't book tickets for others unless you fly first with them (Turkish) as per another member here in the forum, with other airlines I can book tickets for anyone even if I have never flown with them. This doesn't apply if you're traveling also in the same booking.
The surcharges tend to be pretty high in Turkish specially in partner airlines, in business class they seem to round 350-700USD one way. United is 20-150USD and usually in the lower end for the same redemption.
For the routes (DEL-FRA) in business class:
United for 2k INR fees + 63k miles
Turkish 39k INR fees + 60k miles
Singapore Airlines 1.5k INR fees + 62k miles
I surely wouldn't book Turkish for the above redemption.
You'll have to evaluate what is best for your case in terms of value (miles required, fees to be paid), routing and scheduling, availability of award seats and baggage allowances which might make a dent on your pocket too.
My pick on best always depends on the destinations you're interested in.
For me United it's the best: easy to book, plenty of availability, I'm based in T2 city so awards won't cost more, allows me to fly Air India and Vistara so more routes and flights available domestically but slightly more points required, lower fees than most airlines, etc.
Vistara also has very good value in certain routes. PNQ-SIN is 16500 one way which beats SQ in terms of value and routing for me in this specific case. For flying domestically they do the trick most of the time but I still hate having layovers when there's nonstop Air India flights. Another nuisance, is that they have fixed pricing upgrades. For example recently DEL-IXL from economy they asked for 10k per pax for the upgrade, the plane took off with half the business class empty. In Air India I bid 3k per pax and got me and my companion upgraded to business class. Also some empty seats but at least they weren't asking for such a poor value offer to upgrade to business (they were asking basically for the fare difference as an "offer" to upgrade).
SQ is probably ahead of Qatar just because of Star Alliance partners in India (Vistara and Air India) and possibly in the region, OneWorld has no partners in India. Even so United seems to have way better availability online for flights within India and also originating here. Turkish and Singapore should be able to but online award booking shows very limited availability compared to United.
I would avoid any airline outside Star Alliance if you have travels within India or the region unless you have an specific redemption in mind.