You really have to define what you consider to be "best". Under the covers, they're all basically the same. The difference is mostly bells and whistles.
There are a bunch of good, free, straightforward calculators out there. JBM is a classic. Shameless plug: I'm pretty happy with the one I wrote.
But honestly, they're all the same. It's just F = Ma. Pick what does what you want how you want for the price you want.
The ones that have a significant computational differences are:
- Hornady 4DOF. You are dependent on them for the data to use the "4th degree of freedom", which is a misnomer, but commonly used and close enough.
-Applied Ballistics. Uses a different method to get at the same thing as the Hornady. Again, you are reliant on them to get hte data to make the most of it.
-Lapua. A true 6DOF calculator. You guessed, it, dependent on them for the data. The whole app is misguided in my opinion. 6DOF is not the best way to calculate simple trajectories, and we have NO idea how good or bad the data is. Still, very interesting. But I don't get why they put it on a phone.
-Anything Pejsa based. The PRS crowd seem to like overpriced Pejsa-based calculators even though the Pejsa method is basically obsolete with modern computers. Or they did last time I was on Snipers Hide, which was a while ago.
There may be others out there, but I don't really keep up because I think people way overstate the importance of a calculator for 99.9% of what most shooters do. They're more useful as learning tools than shooting tools in my opinion.
For a more detailed overview of what makes them different, I wrote this:
Comparisons of various methods of ballistic calculation, including the Point Mass method, for sporting applications
bisonballistics.com
And this:
A technical overview of Hornady's Modified Point Mass calculator.
bisonballistics.com
Those articles are several years old, and probably slightly out of date, but the concepts are still valid.