Transports carry around all different sorts of cargo, from common ores to precious minerals. In general, the better the transport, the more lucrative the goods it carries. All transports come equipped with guns, come with escorts, and have heavy armor. The higher end of transports have quite good guns, very good escorts, and very thick armor.
They are quite slow, and moderately armored. Most of the time they are found near collector bots, and will attack if you attack them. Unlike collectors, they will spray ion fire at you. Keeping distance or strafing away from them will work.
These bots most often found near static hive queens, and this is when most players fight them (unless you find them elsewhere). They are lighter than their Milanar counterpart, and has less armor. Mounts dual positrons, so if you are not careful, they can kill you fast. They come with escorts. Attack roll will work against them.
Big and slow, mounts dual positrons. You won't find one without escorts, unless someone already killed the escorts. A simple attack roll works fine, though it takes a long time.