I will just mention some of the most popular places for amplifiers and some install basics.
Never install an amplifier upside down, it will over heat!
Under front seats
 A favorite because it has the best security of all others.
 It's closer to the battery.
 Shorter power wiring.
 Minimum voltage drop.
 Amp has to maintain hotter operating temperatures because of less air flow.
 Seat must be removed during install.
 Be aware of wiring running under carpets and in tracks.
 Very close to battery.
 Heat, wasted space.
 Just not a good place for an amp unless it is nessary.
 Fair amount of security.
 Ease of installation, plenty of room to work.
 Better cooling then under seats.
 Small danger of damage during trunk loading or unloading.
Long Power and RCA wires. Higher loss of current due to resistance in the wire.