First of all, if your firstnamelastname.com domain is available, claim it now. Even if you don't decide to use it immediately, it is a valuable asset that you might not be able to claim later.
I would say that firstnamelastname.com is much more effective when people have heard of your first and last name. Until they have, the domain name is not saying much to anyone. I have two main domains that I use. One is analecta.com. Analecta means the same thing as analects, that is "a collection of short literary or philosophical extracts." I chose it as a good site name for a writer no matter what I was writing about.
Curiously enough, my blog is not on that domain. It is on everypageispageone.com, which is the name of my blog and of the book that grew out the blog. Once I coined the phrase Every Page is Page One (which happened more of less by accident) I claimed the domain immediately because I knew I wanted to write the blog and he book under that name. It is now the phrase that I am associated with in the tech comm and content strategy worlds. So that was a case of choosing a domain to reflect the idea and the branding I was developing.
markbaker.com was, naturally, gone long before I thought of claiming it. The curse of having a short and rather common name. I wish I did have it, of course, but I think if I did I would probably be redirecting it to analecta.com or everypageispageone.com until such time as I was well enough known for it to make sense to lead with my name.
However, if I was starting out now I would think long and hard about whether I wanted my own domain at all. I think there is a strong argument to be made that if you are chiefly looking to raise your profile it may be much more effective to publish on an existing platform like Medium or LinkedIn. The advantages of these platforms is that they come with a built in audience and built in facilities for sharing and discovering content. If your stuff is any good, it could find an audience much more quickly on such a platform. The downside is that you give up a degree of control and ownership. But if your goal is to market yourself to future employers, they are much more likely to find you on LinkedIn or similar site than on your own lonely domain off in the corner of the net.
And all this is not to mention that running your own domain is going to set you back some money every year for hosting and domain registration and will require you to master some technical skills to administer and secure it properly. Using a third party site avoids all those costs.