There really is no "one size fits all", even when it comes to hamsters of the same species! Cage size is highly debated amongst all owners, you're going to get a lot of different opinions by asking this question. Just a fair warning before I delve into my thoughts and opinions
The minimum, if you want to possibly add a Syrian, should be a cage of (3,937 cm sq) 1,550 sq in (now people will argue this, but
no other cage size has ever been scientifically proven to be suitable. Only this one). If you have a cage of (3,937 sq cm) 1,550 sq in, it will comfortably house a Syrian down to a robo. However, here's where it gets complicated...
Not all Syrians will be satisfied with this size cage, needing cages that may be (5,080 sq cm) 2,000+ sq in! Besides that, Chinese hamsters tend to be very shy, and do better in a well furnished, but smaller cage. Thus, if you get a super energetic Syrian, you probably should cross a chinesey off your list. Remember though, that a (2,286 sq cm) 900 sq in cage filled with stimulation and deep bedding, is much more suitable than a 1,550 (3,937 sq cm) sq in cage with just the bare essentials! Make sure that for whatever size cage you get, you can pack it with toys, tunnels, and bedding. A large bin system, IKEA hack, or custom aquarium works best for housing Syrians
To achieve (3,937 sq cm) 1,550 sq in, you can try....
A double
detolf from IKEA
3
SAMLA bins from IKEA
Or a custom aquarium that equals 1,550 sq in (3,937 sq cm)
If you'd like to have a cage that's a bit less, overwhelming, you may want to consider cutting Syrians out from your list. For example, a robo could happily live in a cage of just (1,525 sq cm) 600 sq in, while a Syrian would almost never tolerate that. Overall, as an owner, you'll need to decide whether you will keep Syrians, or dwarfs. If you'd like both, that's absolutely fine, but do be prepared that you may be spending quite a lot on housing.
Well why not smaller? Many people keep their Syrians in smaller? I cannot tell anyone whether to get a square metre cage or not. It's your hamster in the end, and if you decide you will keep your Syrian in a 600 sq in cage, nobody will judge you nor attack you for it. However, Syrians really are large rodents (when you compare Syrians to other rodent species, you're likely to describe them as being rat sized. Meanwhile, a dwarf would be more mouse or gerbil sized) and should have decent amounts of space. Besides that, in the wild, they have huge territories and can travel several miles nightly- something a 600 sq in cage just won't replicate. Now some owners will keep their Syrians in smaller, but if you notice, many (including myself!) are constantly combatting things like bar chewing (which like it or not, is usually due to something about the environment being unsuitable), corner digging, pacing, attempting to escape constantly, etc. This is why I highly recommend large cages, aside from that, bigger is better. When it comes to any species, if you go too big, you can always section a cage off, and expand as needed. If you go too small, you'll have a hamster stuck in a tiny prison, and that's just no good! Go as big as you and your wallet can xx
Sorry for the rant! I get very passionate about cage size
If you'd like me to share the studies done on cage size, I'd be happy to! Apologies if I got any inches to cm conversions incorrect, just a quick conversion using google. Remember again that this is just my opinion, and other opinions WILL differ