We have a 5 quart KitchenAid artisan. Ours is pretty old (I think almost 15 years, my husband owned it for years before we got married) and starting to show its age but I think it's definitely worth it. We don't actually bake that often but it is invaluable for certain things (especially kneading dough and beating egg whites).
If I were to buy one today? I'd get the professional instead of the artisan. It has a heavier motor and all-metal construction. This is better for heavy duty stuff like kneading bread. Our artisan is definitely starting to show it's age - it has started wobbling a lot when mixing heavy things like dough (which means I have to keep a hand on the head when it's kneading so it doesn't walk away across the counter). But like I said, it's 15 years old, so I think it's had a good run of it.
I saw the mini one at Target the other day. I would not get a mini one. It was the same price as the 5 qt artisan and has a smaller motor and I do not think it would work for heavy duty things. If you're worried about being able to make small batches of things, I make 1/2 recipes of things in the 5 qt all the time with no problem. I think there's a smaller (shorter) bowl you can buy for the 5 and 6 qt mixers as well.
ETA: If I didn't have it, I would probably never bake any bread that requires kneading, anything that requires creaming butter + sugar, or anything that requires beating egg whites. I am lazy plus it is hell on my bad wrists to do those things by hand or even a hand mixer.