None are the best. Some are better choices than others for a small tank.
For example you should only buy fish that only grow to 1-2 inches, like a betta, zebra danios, some types of tetras like cardinals or neons, etc... DON'T BUY GOLDFISH for a small tank. Contrary to popular belief they are actually messy fish and grow quite large and so need a large tank.
I'd recommend a 10 gallon tank, which you should perform a fishless cycle on before adding fish (read http://www.fishforums.net/index.php?showtopic=113861 to learn how to fishless cycle). This will make sure your fish are healthy from the get-go. A cycle will happen in every tank, you can't stop it from happening, and it's a good thing, but while it's happening, your fish will be stressed and possibly get sick and die. That's why a fishless cycle is recommended. That and it's a lot easier! It's just less gratifying becuase you have to wait 1-2 months before you can have fish, but this way you have to do less work, and they don't die on you!
Then I would recommend buying a betta, or a school of small fish. A betta would be happy in 10 gallons. A school of small fish also would. You could get a school of neons, or some small catfish (pygmy corydoras comes to mind!) Or you could have some shrimp, but be careful because they reproduce quickly! Same with guppies.
Zebra danios are a pretty and hardy fish, you could have some of those.
The 4 essential things you must buy before buying fish: 1) fish tank, 2) filter, 3) heater, 4) LIQUID TEST KIT THAT MEASURES AMMONIA AND NITRITES, most people miss this one. Ammonia and nitrites are toxic to fish. You need to keep the levels at or near zero. This is what fishless cycling will do for you! If you don't fishless cycle you will need to change the water many times a day to keep the levels low.
This is annoying to do and time-consuming and water-wasteful!
And don't even bother with test strips. They are a waste of time and worse than bad, they're misleading. Plus the price tricks you. A liquid test kit will do hundreds and hundreds of tests. It costs more up front but it will last you over a year. While a test kit, contains maybe 5-25 test strips. That's a really bad value for your money and they don't even work as well as the liquid kits!
One last thing... I would do ALL your research online instead of consulting fish shop employees. First of all, their primary interest is to sell you stuff. On the internet with research, nobody is trying to sell you stuff, we are trying to educate you and keep your fish healthy, we have no other motivation. Fish shop employees are taught things, not for the health and safety of fish, but to try to sell more things. They will very frequently tell you all sorts of inaccurate lies in order to try to tell you something that means you will buy more fish, more equipment, and they will always try to keep it simple so they don't confuse you and turn you off.
For example, fish shop employees will often tell you you need a pH test. You don't really. It's -nice- to know what pH you have, but it doesn't really affect anything, to be honest, and they often blame illnesses on pH... when it doesn't really matter for 95% of fish, they are pretty adaptable to pH. But they are not adaptable to ammonia and nitrite. But pH is something everyone knows what it is and everyone understands, and they can sell you stuff to buff it up or lower it... so they like telling people that the wrong pH is making their fish sick.
