So I started desktop. I have had desktops since I was pretty young. Laptops, too, now that I really think about it, but basically I was given hand-me-downs that would be replaced when they croaked as a kid. (Except for my first desktop, a barbie themed one marketed towards kids.) I namely played Sims on the desktop, though I remotely remember having Stories on the laptop.
Anyway, this continued through a series of hand-me-downs until a little after the launch of 4. Around then, my desktop was outdated and I began a much more mobile form of life. So I had a laptop for school and Sims 4 was supposed to be fine for laptops. *shrug* I kept up with 4 on it, but space was limited so I couldn't port 3 over. I attempted sometime later when this laptop was driving me crazy with its limited space (and other odd malfuctions) to take in another hand-me-down, a desktop, and while space was fine it was in another league of outdated in comparison.
So everything eventually culminated in actually purchasing a proper laptop, one that is beefed up enough to practically be a desktop. (Huge, two chargers, Sager, etc.) However it is still technically mobile. Not very mobile, mind you, but I always thought laptops were a hassle to bring anywhere anyway. It just matches my previous thoughts and feelings perfectly.
My conclusion? Both work. In general, I like desktop set ups better. Laptop mouses are annoying and if I have to go laptop it theoretically means I don't have an assured desk to work with. But a normal PC mouse and desk can always be added to a laptop, while a desktop always needs a fair bit of space (I have set one up on a coffee table before, so it is theoretically doable to find random space). It more depends on the specs than the setup/accessories, because they crossover. I'd take a good laptop over a bad desktop any day, or a good desktop over a bad laptop.