For casual I use the one at "Big Game Info". It is easy, prints a good output and is quite accurate. When I want to get down to the "nitty gritty" I use the one I developed in the 80's. It is crude, not user friendly by todays standards, but it was noted by the military in Virginia to be the most accurate one they had access to. It sold internationally for a period of time.
I can do out to 1500 yards, extremely heavy and light loads, multiple sight ins (for the sight in of a squib load based on the sight in of a hunting round), all the environmental conditions, elevations, up/down angles, wind at all angles. I can back calculate muzzle velocity from a chrono velocity, and a few more obscure things nobody else would be interested in.
The one thing I didn't do, and wish I had, was to automatically calculate the clicks up for range compensation. Would have been very simple to do, but now the programming language is obsolete and I am not about to resurrect it.