Horses for courses here: I have the aforementioned Stanley knife for the heavier work, such as cutting thick pieces of plastic. But I've used one for most of my hobby life (which began at around 10 y/o), and for the first one and a half decade or so, it was my only blade too.
When I got my first metal miniatures (A pack of Space Wolf Blood Claws), I had just one army; Dark Angels, so I used this big Stanley knife to dry-sculpt them back into standard marines. And I did a pretty good job at them too, all things considering.
Imagine shaving down, layer by layer a metal mini, and then sliver by sliver carving new details in the new surface...
Soon after though, I got my first 'true' hobby knife. And going by the above posts, apparently, X-Acto and scalpel blades are not the same, so I won't be able to identify it as either.
But it has a thin, aluminum handle, with a screw on, textured, tube, which secures the cross shaped bit that holds the disposable actual blades. It holds blades with a thin tang, as opposed to the blades that come with a very cheap set I got about a decade ago, which have a wider tang and will not fit in my original handles.
These fit in either a wider version of this aluminum handle (but with a plastic cross shaped bit), or in a larger, (red) plastic handle, on which the only metal part is the textured crew on tube.
I do not particularly like these, but for several years, the only blades available locally were of the wider variety, to I was forced to use the aluminum handle from this cheap set. It eventually broke (not surpisingly, the plastic cross bit, which had always been somewhat loose to begin with).
So I would certainly not recommend these ( I suppse they're aimed at the scrapbooking and cardmaking crowd, and are not made to withstand very hard work). The sets, which can be found in Poundland, Action, etc, do come with blades in a variety of shapes, but I've always found only the triangularly shaped pointed ones of use. But obviously, that's all down to personal preference.
A couple of months ago though, I bought 100 of the smaller tang blades for just €5,- on AliExpress, so replacements will not be an issue for quite some time.
I do find they are more brittle and tend to dull faster than the ones bought locally, but this is something I can live with. Compared to being forced to using a single blade for close to a year, until it
really won't even cut skin anymore

, this is quite a luxury.
But I'm still stuck in the tradition of having two handles; one with a fresh blade in it, and the other with one that has been chipped and dulled. The fresh one is for delicate and precission cutting, while the old one is for course work, such as cutting up sprues, scraping surfaces, prying bits apart etc, etc.
So, as far as recommendations go: use the right blade for the right job. I have on standby, for different jobs:
- an old potato peeler (which I sharpen as required) for cutting large foam blocks
- a Stanley knife, for heavy duty work
- a small handle with a fresh blade
- a small handle with an old blade
The first two are self-explanatory, but the smaller handles might take some sourcing. The disposable blades can be easily found on-line (I've used AliExpress, like I said), but the handles might be more difficult (although not by much). The handles might also be down to personal preference, as there are quite a few types out there.