If you get it skimmed, than you get a great finish, easy to paint, and dead easy to patch if you have work done.
If you paper and paint, that's far more work, the joins and edges will show (yes they will, they always do) and anything you have done ( new windows, a new socket, an accidental dent or any other damage) will be a complete to cover up, you'll always be able to see the bodge.
I've had to hang wallpaper at work on false walls, though thankfully not often. I hated doing it. I hate it even more on actual walls because they are never square. Even with thick lining paper, you need to do some filling anyway if you have 'surface of the moon' walls.
If you can't afford to have it skimmed, then I'd fill it the best I could, paint it and live with the bumps until either I could afford it or I stopped noticing the bumps.
In this house I've done a mixture. 100 yr old lime, where sound, I've filled and painted (once I got the poxy wallpaper off it). Used claypaint, which is very matt, and TBH though I'm very fussy about things like sharp clean edges of paint, I don't notice a few small irregularities in the old painted plaster after a few weeks anyway- it's part of its character. Plasterboarded walls with dot-and dab, those we stripped off and had redone with modern insulated boarding on battens and skimmed. The decent modern plaster walls I just stripped the paper off, filled any small holes from picture hooks and rewiring, and painted. Where there are patches of badly damaged/blown lime, like on a chimney breast and under a bay, we're taking it off to the brick and having it patched then the whole wall skimmed, all with modern lime.