The question is two-fold. Firstly what constitutes a 'pet', and secondly are pigs really that great?
'A domestic or tamed animal or bird kept for companionship or pleasure and treated with care and affection'. There's a definition for you, and my dog fits very squarely into it – he's a great companion (I know I feel low when stripped of his company, which is very undemanding), he brings me a lot of pleasure, especially when invited or when he gets something right or gives one of those looks (dog owners will understand). From my dog I get comfort, security, a couple of good walks every day and a feeling of well being. A dog makes a great pet, but they're not everyone's cup of tea (I do not like cats).
But what about the pig? He or she starts cute, grows big quite quickly, makes a mess if you do not look after him properly, and has an inquiry that borders on the destructive. You can train him easily, he'll be as biddable as a dog, and will approach you as if you were a pig, expecting several meals a day, plenty of contact (scratches, rubs, and the opportunity to nuzzle), and distraction / boredom relief on tap. The trouble with an active mind such as that operating within a pig's thick skull is that it needs stimulation. Questions such as "what does this taste like?"; "what's in here?"; "what's under this?"; Egypt "what happens if?" compete with "what are you looking at?" and "where's mine?" all the time in a pigs waking hours.
Pigs snore, they catch diseases, they bite (as in testing and tasting and not knowing just how great their jaw clamping force is) and they bring great pleasure just by being. They are a demanding pet though, and need companionship. They will not do well indoors, as they need to root around and there's only so much you can do when the base is floor-boarding or a concrete screed. I guess carpeting would be an interesting challenge.
As for care and affection, they need a surprising amount of the former, and have a different way of showing the latter, which can get quite physical and involve teeth. You can train them to a harness, but pigs are not built for the type of trek that a dog provides: I doubt if a pig would get out of the garden gate easily – too many tings to find out about.
So, a pet, yes, possibly, although requiring a quite different approach to the dog in your life, and certainly a completely different proposition to that presented by a gold fish, a bearded dragon, cat or ant-farm. But a 'great one'? Probably depends on how much you love your bacon.
