Is the length or the shape of the antenna more important?

I live in an apartment and can't put up an outside antenna. The Grundig
YB400PE I just bought came with one of those little wire antennas that winds
up. You attach one end to something, and spool out the antenna to the radio.
It works, but no so well.

I was thinking of making my own antenna out of some wire, but my apartment
is of limited size. So, I was wondering if I could run it around the outline
of the apartment. Maybe up at the junction of the wall and ceiling, hidden
in the "joint" there. But then I got to wondering if that would defeat the
purpose. Wouldn't a straight line antenna work best? And wouldn't the
antenna work best it was was parallel to the "line" upon which the signal
propagates?

Sorry is these are dumb questions. I bought the antenna to entertain myself
during the recovery period after an upcoming surgery and I want the best
possible reception.

Thanks in advance.