(Spring Antenna).
the mantra of RF guys: solve RF problems with antennas first. they are cheap, they are easy, and they produce the greatest effect for the least cost and effort
433 mhz is also a ham band. googling 70 cm antenna will keep you busy all day.
short and simple:
one to one, fixed locations, use directional gain antennas on both ends
one to many, fixed locations, use an omnidirectional antenna on the one end and directional on the many
one to any, mobile, useomnidirectional antennas
the easiest omnidirectional gain antenna to build and use is the collinear. good for up to 15 db of gain. anyone claiming more has knowledge of the laws of physics he is not sharing, or he is a liar
the benefits of gain antennas work equally well on both ends of a link. if you stick up a 15 dbi gain antenna, every link gets 13 db gain over a standard issue 2.14 dbi gain dipole, on both ends