Stand mixers: plastic or metal, with 4 to 7 quart glass or metal bowl. Tilt-head vs. bowl-lift.
When my plastic hand/stand Hamilton Beach mixer broke, I decided I deserve the Real Thing. Real thing turned out to be gray metal KitchenAid Professional 520 mixer with 450W of power, 5 quarts of bowl, and a bowl-lift system. Larger models would be difficult to fit on kitchen counter. It costs about $300 at Amazon and looks and works like a smaller version of an artisan bakery mixer. Which, in fact, it is: KitchenAid makes mixers used by bakers and cake-makers. I saw one on a tour of Zingerman's bakery in Ann Arbor. It also turned out that I need an additional small hand mixer ($15 generic from the supermarket).
I bake a lot, both bread and light whipped cakes. I choose a stand mixer over a hand-held one because the bread kneading as well as the egg-beating takes long time, which I could use. The combination hand/stand, as I mentioned above, broke. To put accurately, combinations are hand mixers with a stand. That means they should be lightweight and small, and that limits their mixing power. Good engineering plastics cost more than steel, and cheap plastic mixers are made of cheap plastic which breaks and scratches. Stand mixer can be heavyweight, and better ones are made of steel. Mine weighs over 20 pounds.
All stand mixers come with several beaters: a wire whip for high-speed whipping, a flat beater for the heavier, thicker cookie dough, and a dough hook for a low-speed kneading. Most of stand mixers have an attachment hub. KitchenAid sells meat grinders and juicers as attachments.
You can get the tilt-head or the bowl-lift mixer. The former tilts back and lets you remove the bowl clearly. The advantage of this design is easy access to the bowl. The latter has the bowl suspended on the lift hooks. You bring it up to beat and lower it to remove. Getting the bowl out the mixer is tricky: usually I have to remove the beater with one hand and take the bowl off the hooks with another and take both from under the mixer at the same time. The advantage of this design is lower clearance. The mixer takes up lots of counter space as it is, and fits under most wall cabinets only barely. With the tilt-head design you have to pull it forward from under the cabinet, or keep it on the open space. To keep the stand mixer in the cabinet and to take it out than needed is not practical. Also, large professional mixers are all bowl-lift (but with bigger clearance for the whip/bowl removal), and I presume the maker already knows how to do it well.
As I mentioned above, I still need a small mixer. Some recipes take combining two pre-beaten mixes. Sometimes I need to beat small volume, and 6-quart bowl is just too big for two egg yolks. Sometimes I need just a little whipping, like for whipped ganache, and it's hard to make it light and well-whipped and in small volume at the same time with a big mixer.
See also: kitchen, kitchen knives, frying pan, coffee grinder.