I can't help but say this so...
"Can't we all just get along?"
The Airspy/SDR#/Youssef situation needs to come to a halt, that's my personal opinion on the matter so there, I said it.
Anyway, back on topic:
I would agree with pretty much everything Flatliner said about SDR-Radio aka SDR-Console. It is without a doubt the most feature laden and complex program for SDR work on the Windows platform at this time - having said that specifically, however, with it having so many features and being so complex (because it really is) it's also the most capable software available, with regular updates and as Flatliner noted actual support from the one and only person that develops it, Simon Brown (that I know of, I don't think there's a big huge developer team, I think it's all him but I could be very wrong on that aspect).
I LOVE that program, I really do, and I hope soon to have an SDR hardware device that can make the very best of it overall and so far that's going to be SDRplay aka the RSP. I'm not faulting Airspy, really, and I'm glad it's been successful for the creator/developer just as SDR# has been, but at this point in time the pros/cons list I made for myself in deciding which device to buy 'cause I really can't afford a HackRF which is what I'd take in a split second if I could actually afford it. The pros vs the cons for the SDRplay put it well ahead of Airspy in most every respect even in spite of the recent issues with support for that device with SDR#. If it gets supported, great, if it doesn't well, I've got SDR-Radio to work with and it can do the tasks just fine too but it obviously doesn't have the kind of plugin support that SDR# has built up over the years.
I checked out CubicSDR recently when I saw it mentioned here and yes it's very basic but development is in progress as noted.
HDSDR is another one that's been around for a while but I don't find it appealing - that's my own personal opinion of it, and it's tempered by the fact that I haven't spent a great deal of time actually using it and learning the ins and outs that it's capable and not capable of. The very first time I used SDR# almost 2 years ago I had it functional in seconds, literally it was tuning in my NOAA weather frequency in under a minute of starting it up without issues so it has been the go-to SDR app for me for a long long time and still is in most instances.
There are others on other platforms too, like Gqrx (almost an SDR# style clone, it's NOT a clone but it's similar enough to get up and running in a minute or two for most people after they've gone through the somewhat involved compilation/installation process on their distribution of choice, even OSX can make use of Gqrx).
And of course there's SDR# which is the most popular (by a very wide margin I would guess) which has the largest collection of incredibly useful plugins to make it a pretty complete "suite" I suppose. It gets the job done and that's really all that truly matters when you get right down to it.
I'm hopeful that as time passes we'll find newer pieces of SDR software applications that increase the usefulness of the technology and add a lot more functionality on top of what's already possible even now, it just takes creative talented developers to imagine what they want to do and then code it up.
To the question of is SDR# the best software to start with well, whenever someone uses the term "best" it can be problematic because someone
else might immediately counter that they think something
else is better so, you can see how that degenerates into babbling and rambling pretty fast.
Do I think SDR# is a great starting point for people interested in SDR? Damned straight I do, it was my first point of entry into this new way of monitoring and it's easy to get working (not that other software isn't, mind you), and the wealth of plugins - even in spite of the manner you "install" plugins - make it "the best" (there, I said it) point of entry in my opinion.
It's not like you can't install any SDR software you can find for your platform and then
try them all out yourself and find out what works BEST for you specifically because you're the only one that can do that. With Windows being the king of the hill obviously there is many more applications available at this time, with Linux having applications too, especially the GNURadio framework which can do most anything given the time and effort to make it happen. OSX also has capabiities too - iirc the guy that created and develops HackRF actually does all his software development for HackRF on the Mac platform using OSX and Linux as required but I might be wrong on some aspects of his particular usage so don't hate me if I am off a bit there.
Hope this helps...