I'd go with a laptop. 15 inch monitor is plenty if you're not doing movies or graphics on it, it's plenty big enough and a pretty good one can be had for 600$, watch for sales at places like staples.
You can do computer on the kitchen table, in the living room, the bathroom, the bed room, while traveling etc.
You're on the internet and people show up un-announced, you close the lid, put the computer away and you're done.