I have cats and dogs (two of each) ...
Depends on the kind of person you are...
Cat will look after it's self all you need to do is feed and water if its a stay at home cat you need to clean out the litter and be prepared for the house to stink of cat shit till you do clean it. Also if you rescue a cat you need to keep them indoors for 3 months so they get used to the "smell" of your home and IF you do let them out they know to come back to you..
Same if it's a kitten you get you need to keep them at home until they can go out. If you get a BOY get him fixed ASAP other wise he will start spraying around your house from 12 weeks and once that start's he won't stop even if you have him fixed so enjoy cat piss EVERYWHERE.
If you want to keep it home then it's no problem either you do.
Dog needs way more care if you ask me and I love our two (English springer spaniels) depending on the size of your dog depends on how much he/she eats and the cost involved. Where you live and if you are in a flat or have access to a garden. Dog needs to be let out to use the toilet so in a flat this could be a "choir"
They also need to walk at least twice a day, they suck if you keep them at home all alone. Some dogs can't cope with it and will destroy things because they are not being exercised / entertained. There are no bad dogs only bad owners. So if you are happy to go out every day rain, wind, cold, heat and shine and pick up dog shit then go for it
As a pup they will chew EVERYTHING - (
a kitten will claw everything!) if you lock your dog up and he/she gets ill they will shit everywhere a cat will do this also but has a greater chance of getting to cat litter than a dog just doing it on your floor.
Dogs need to be trained. You need to teach them to sit, stay, not to jump on people and when to get "off" people* and YOU MUST BE consistent with the training, any words you use for "off, get away, back off, down" whatever it might be you and everyone in the house needs to use the same word.
*that's just the basics

They can do some cool things. Both of mine will listen to only me on a voice command and hand signals but will listen to everyone if you use the correct whistle pips
Dogs also with food there is a lot of crap in dog food much like human ready meals so do some research anything with I think vitamin B or loads of it will lead to a hyper dog unless you want them working (both of mine do) so they have the fuel to go all day.
Note: If you want to get one of them stupid dogs that are no bigger than a cat. Get a cat.
I love both my cats (we had 3 one died earlier this year) and both my dogs. As much as I love both my dogs and always had dogs, I'm a cat person.