I have a 700 square foot apartment with carpeting and a cat...
the best vacuum cleaner by far is called the Tri-Star.....it is expensive but it truly works better than anything out there....
I would get a bagless one. Less costly in the long run, you don't have to worry about running out and buying bags. Mine came from walmart - works great 5 yrs later. I have a dog.
Vacuums are like cars everyone will have a favorite. Dyson is most likely the most expensive. as far as the best they all have their good points after years of use where I work we ended up with a sears vacuum (link below) it works very well it is under $80 so we can replace it as necessary we have used commercial vacuums at $800 each and the sears cleans just as well . We get about 18 months use out of these and about 5 years out of the commercial vacs our vacs are in actual use about 7 hours a day (we have a 24 -7 operation) I have one of the sears at my house have had it for 4 years still working just fine. My suggestion to you is to go to sears and compare the different vacs they have all brands. Pick the one that you like the best. they all have a different feel you might not like one because it feels heavy or too light, hard to push, awkward attachments etc. Good luck on your decision
Hoover. Something small yet sporty...maybe in a cherry red model.