Make the decision based on what you need, because the two options are very different.
Side runners or "side steps" are there to provide a step, to help you get into the vehicle or to reach the roof. They offer no protection from rocks, and can actually increase damage to the vehicle if you get hung up in the rocks. This happens because side runners reduce ground clearance, making it more likely that you hit a rock, and the impact to the side runner can damage your rocker panel, and maybe your door. Side runners are a great option if you need a step, and don't need protection on rocky trails.
Rock sliders are much heavier than side runners; they are made from steel that is strong enough to support the entire vehicle. They offer protection to your vehicle when off-roading in technical rocky terrain. You can jack up the vehicle using the rock slider as your point of contact - that's how strong they are. But there are downsides: (1) they are heavy (sliders this length will weigh between 100-150 pounds for the pair - depending on construction; I haven't seen a weight provided by Ineos), and (2) they aren't great as "side steps" due to the angle at which they are mounted (which is intentional, as it maximizes ground clearance and the ability to slide over rocks). So you get reduced convenience as a step, and reduced payload in your vehicle due to the weight of the slider. Rock sliders are a bad option unless you need the protection.
Here are a list of rock sliders that I checked-out for my 2017 Tacoma. The columns are (1) Manufacturer, (2) Material: the main difference is strength. HREW (hot rolled electric welded) metal is milder steel, which is still plenty strong, with a yield strength of 40ksi. DOM (drawn over mandrel) steel is the same material which does not have a welded seam, with a yield strength of roughly 70ksi; and (3) Weight in pounds for the pair.
CompanyMaterialPoundsRCIHREW120CBIHREW110CBIDOM130PelfreybiltDOM / HREW100Metal TechDOM132All Pro?120BAMFHREW?MobtownDOM150
