It depends entirely on what you do, and how do you do it.
Pro for a second screen:
- you can view (more) docs, code, and output at the same time
Pro for SSD drive:
- much disk intensive stuff is faster, e.g., compilations
If what you do is something like developing web sites, where you need the UI code, the backend code, a browser, and some log files open at the same time, then a bigger screen is probably a better idea.
If, instead, you do something like debug large applications in compiled languages, trying to find which revision broke things, and git bisecting until you find the right place, then perhaps an SSD is better.
There's other things you might be able to do instead. For example, more RAM might speed things up more than an SSD. Or you might buy books or a training course. Or you might buy a second laptop, used, and dedicate all your computer activities that are distracting you from your work to that one.
Or you might save the money.