For years, I would only ever have a laptop but PCs in those days weighed as much as a dinosaur and had the appeal of a block of concrete. I remember with fondness my first laptop back in 1993 and the land of DOS. It was a sleek Toshiba which served me very well. Five various laptops later, I have finally been persuaded to buy a PC so I think I have enough experience to answer your question. If I understand your question correctly you are concerned about the effects of sitting in front of a computer for long stretches at a time. You are right to be concerned as computers can really affect your health and can cause back pain, wrist strain, eye strain and exposure to electromagnetic fields (this last is an unknown quantity but you can place a piece of amazonite or sodalite stone next to your computer as these are said to neutralise the noxious effects)

The advantage of a PC is that you can place the screen at any distance and in any position (right, left, in front or even above) you find comfortable whereas the laptop restricts you to the distance you can comfortably use the keyboard which will be a lot closer. To reduce eyestrain remember to blink frequently and to focus on objects at different distances at intervals.

If you use a dedicated computer desk with a pull-out shelf for the keyboard, this will greatly reduce backstrain as you can type with your elbows close to your body. Unfortunately, your laptop cannot fit on that shelf and you will have to either put it on top of the desk (if you do a lot of typing you will soon feel your back protesting) or on your lap but beware that some laptops get incredibly hot even if you put a tray underneath.

When you use a PC you will automatically have to use a mouse. I used to have terrible wrist, neck and arm pains but I have magically solved that problem by investing in a mousepad with gel wrist rest. it really works and there is no reason why you can't use a mouse with your laptop as well. The touchpad which comes with laptops can cause a burning sensation in the finger you tap with and can be a bit difficult to use for certain games.

The great advantage of the laptop over the PC is that you can use it anywhere and if space is at a premium it is a much neater solution, despite the much slimmer screens, PCs still take an awful lot of room. However, if you are worried about the effect on your health of sitting in front of a computer for hours, I would opt for the PC. You should still schedule regular breaks, walk around, do neck and shoulder rolls and make sure you sit upright on a comfortable chair with your feet firmly on the ground.

I would also say that laptops have a shorter life than PCs. Because they have smaller memories, they get clogged up much quicker and become slower. Also, moving a laptop around means that there is more likehood of damage (the catch broke on 3 of my laptops). Your PC is made up of components so you you only need to replace that component. If the screen goes on your laptop, you have to replace the whole laptop.

All things considered, I think that unless you are often on the move the PC will be more durable and versatile and should cause you less stress.