Stay with Linux.

It's really a personnal question, and depends on your preferences on user interface.

For example, I prefer the emacs user interface and I use emacs with ratpoison as window manager on X11 on Linux. I also use emacs on MacOSX (and http://www.emacsformacosx.com is a very good GNU emacs distribution), but I miss the rest of keyboard interaction allowed by ratpoison (which if you stay inside emacs, is not a big deal). I also use X11 on MacOSX. In my situation, Linux is quite preferable. On the other hand, since I'm currently working on a MacOSX application, while I could (and actually did during a period) edit and compile it from the Linux box, I'm currently using the MacOSX box to work on it (and therefore accessing my Linux workstation thru X11 on MacOSX, since it's more convenient than moving around to the Linux box).

This later note, to mention that you can have a setup where "the network's the computer", that is, you actually use the workstation at hand just as a window on the whole network. With a window system like X11, you really get a smooth experience having processes on the various computer on your network displayed on your screen. Then it doesn't matter what OS your current computer runs, you are just using X11 apps, running all over the place.

And if this is your approach, if you're using more a network of computer than a single isolated computer, then consider that (while NeXTstep DisplayPostscript system provided such network independance and indirection), the only window system nowadays providing it is X11 (which you can use on unix as well as on MacOSX or MS-Windows). Also, and for somebody who uses the keyboard 12 hours a day, I notice that I can more easily configure the layout of the keyboard with X11 than with MacOSX (or worse, MS-Windows), and furthermore, I find that the keyboard is more responsive when processed by X11 than by the MacOSX system, notably in the handling of modifier keys (and that, with a DasKeyboard-3 keyboard, which has 6-key rollover (thru usb)!). So when typing some kinds of text, I really prefer to use Linux than MacOSX.

On the other end of the computer system, there's the persistent storage, and on this side, there's some justified criticizim of the MacOSX file system (HFS+) compared to the much better Linux (or other unix) file systems. This may be a reason to want to use a Linux workstation, but you may also just store your file on a NAS (or just a NFS or Samba server on your Linux box), so again, the network's the computer, and the choice of OS on your workstation is not so relevant.

There's the question of the hardware, with multiple considerations. Ignoring the question of price, there's the question of ease of use. MacOSX seems to provide a "it just works" experience, which is good, but on the other hand, if it fails, you may have a harder time than with Linux, where you can usually repair it. For example, sleeping a laptop, or switching to new wifi networks, are no-brainers with a MacOSX laptop, but I've spend hours configuring linux laptops to do that. Perhaps there's some hope and light at the end of the tunnel, in the form of the Libre15 laptop? https://www.crowdsupply.com/purism/librem-laptop

Now, perhaps you will have to test your web development on a Safari browser. Then you will need a MacOSX box to use it, and happily, MacOSX can also run Firefox (and Chrome, etc).