It really depends on your situation.
For my fermentation chamber I figured like prand that an upright is better, and a chest freezer for keezer.
Also for me space was an issue. I have plenty of vertical space in my garage up to the ceiling, but space on the ground is at a premium only having a 1 car garage. So having a tall and thin stand up freezer was the easy choice for fermentation.
The more difficult thing was finding a frost free upright on craigslist, i wanted a freezer not a fridge for the extra space and easy ability to cold crash and lager at low temperatures without running too hard as most fridges aren't meant to get that cold and hold it...they can but it can stress them. Most upright freezers run their chilling lines through their shelves, which makes them immovable and they are usually at horrible locations that wouldnt allow most fermenters to fit properly. Setting up a free alert on the "Upright Freezer" search on my Local CList though and within a few weeks i found the perfect freezer. Granted I may have overpaid at $100 for a 6 year old freezer, but it was literally exactly what i needed space wise and had no permanent shelves. Also at least around this part in Oregon most people way overvalue their freezers on CL so $100 was a steal...its JUST tall enough to fit two of my 30L Fermentation buckets and a blowoff container, not much else. Built a tiny shelf out of some spare wood my parents had laying around and bam, ferm chamber.
Also having the shelves in the door is nice for bottles. I don't bottle much anymore unless its to take beer somewhere and it doesn't get finished, so it creates a nice place to stash those bottles to keep at sub 70F temp for storage when there's no room in the house fridge.
tdlr; Upright all the way, if your buying used though know it may take longer to find one that doesn't run its chilling coils through the shelves.