Having lived this situation lasting a few years in Paris area, I could note the difficulties which one can encounter in a large city.
The few antennas described here allowed me a HF activity with good results taking into account an environment provided in obstacles and parasites.
For the development of these antennas, the ideal is to use an antenna analyzer or a noise bridge. Here are some useful links:
MFJ202B from MFJ
RX100 from Palomar (no longer available)
VA1RX from Autek (no longer available)
MFJ259 from MFJ or MFJ-223, MFJ-225
miniVNA HF/VHF (on PC).
AA 908 from american qrp club
A project by VK5JST
A description by VK5BR