Tetra or guppies?

I have a 10 gal fish tank. I used to put goldfish in but I think the
tank is too small for them. I then changed to guppies, but a cold spell
wipe them out. I am not thinking whether it is easier to put some tetra
(neon red and blue ones) in, or put guppies again.

This is also a sort of a feng shui tank so if any one knows of whether
guppies or tetra is ok, please let me know. Also, advice of colour of
fish and number will be helpful. Concerning the number of fish, I don't
have a big tank, so I can't have a lot of fish (that's why I am trying
to see if smaller fish works).

Thanks for any advice!