This could be a very long post from me, but instead I'll try to keep it short.
There are a ton of factors that go into determining the "best" software, but fundamentally if you ask a CMM programmer, their answer will invariably be the one they know.
If you're running a DCC machine, the best software choice for you is probably the one put out by the company that makes your controller - PC-DMIS for Hexagon controllers, MCOSMOS for Mitutoyo, etc. I've seen lots of problems over the years with OEM software not working very well on another OEMs controller.
Another factor would be how you use your CMM, quick checks, full layouts, production runs, CAD based programming, etc etc etc. Different software has different strengths. The outfit you're buying from should be a factor, too. Distributors tend to be much more customer focused and will help you out early on.
Some people will shy away from 3rd party retrofits, I'm somewhat partial to them. The top two 3rd parties out there are Modus (Renishaw, based on Camio) and CMM Manager (originally IQ Metrology, now part of Nikon).
One thing that has always bothered me regarding the sales process of CMMs (particularly the software) was the promise of having people walking up to a machine they've never used before and being able to do complex programs. These objections tend to get dismissed as CMM programmers trying to overvalue their jobs and experience, but I can assure you it isn't. There is no "simple to use" software, there's only "simple to abuse" software - you need to know what you're doing, and that takes hands on experience. A good CMM programmer is equivalent to a good CNC setup guy. If you wouldn't send someone who's pushed buttons on a CNC and knows how to read print to training for 3-5 days and expect them to come back and immediately start programming complex parts on the machine tool, you shouldn't have the same expectation of a programmer. (Sorry, I'll get off this rant)
To simplify - don't buy into the salesman's promise of trained chimps programming complex parts. The demos always look good because the person doing it isn't writing a program, they're just trying to wow you.
OK, that said, I believe your best options are (and I'm basing this on the assumption you have a B&S DCC machine) PC-DMIS or CMM Manager. The former because it's the OEM software, the latter because it's a strong product with stellar customer support. I've seen someone ask a question on a forum like this, have it analyzed as a bug, and a (free) patch written by the OEM in the space of four hours.
And FTR, I've programmed in Measuremax, PC-DMIS, Aberlink, Geopak, MMIV, and another I can't remember off hand. I've had experience with CMM Manager and Modus, I have a seat of CMM Manager on a computer somewhere that I've never really played with. Of the ones I've actually programmed, I prefer Measuremax, but since that's specific to Sheffield controllers and is obsolete....