Well, let's put it this way. When you take a bunch of street samurai, you can always expect just about the same thing. You will shoot people and you will whack people and I guess throw some grenades every now and again. Street samurai are full-combat blokes, and they don't offer anything else. Fairly predictable, in a way.
Riggers and shamans, however, add a bit of a gamble. Activating the rigger's drones basically gives you 2 more dudes to control, just that they are less sturdy and have less firepower. But the drones can access vents and flank enemies, do hit'n'runs or go ahead as bait. The shaman conjures spirit, both from the environment, if spirit links are present, or from consumable fetishes. But each turn the spirit has a rising chance of breaking free and either vanishing altogether or rebelling and going on a rampage.
Then you also have the decker, who can access Matrix terminals and fight ICPs in cyberspace, all TRON style, digging up dirt that you can later exchange for additional funds or karma. But the decker is generally pretty shit in combat, so you kinda offset the post-run gains by adding combat difficulty.
Also, generally the most important factor to take when measuring combat difficulty is whether you take a Mage with the heal spell to the run or not. Heal almost (almost) invalidates the existence of medkits if you are careful and crafty. They also have superpowerful nuke spells, but they eat all AP, so the mage requires proper positioning. And joke's on you if you miss the fireball and launch it straight into your d00ds.