In particular, GURPS 4E vs. Shadowrun 5E.
Finally making a return to one of the first systems I ever played in (the one with the GM who had every combat as near TPK, that I usually averted unexpectedly by way of application of dakka).
Finding lots of interesting things in how differently the same thing can be handled, such as shooting.
In GURPS 4e, the more lead you throw, the greater your chance of a hit. With a lot of weapons, it's actually not possible to score a hit with all shots (a microSMG for example generally has RoF 15 or more, but even with an effective skill of 23 and a critical roll of 3, assuming the standard recoil 2 of SMGs, you have at most 10 rounds on target). In Shadowrun, it's basically never even contemplated how many of your rounds actually connect. Higher rates of fire (Semi Auto Burst, Burst, Long Burst, or Full Auto Burst) give a varying penalty to the defense roll to get out of the way of the flying rounds. More successes assumes more rounds hit, at +1 to base damage value per each. All recoil in Shadowrun is treated pretty much equally.
GURPS and Shadowrun both have a sleeve rig holster that gives a bonus to Fast Draw/Quick Draw. In GURPS, it can only take holdout pistols, and makes them slightly bulkier as a unit (-1 to Bulk). In Shadowrun? Can take up to light pistols (standard pistols, based on stats and performance. One listed gun, the Beretta 201T, is basically a Beretta 93r with no compensator, a lot of advancement in the 100 years since the 93 came out), and makes the penalty to find them when concealed one greater. While slightly ridiculous (what kind of modern sleeves are roomy enough to fit a fullsize pistol?!), I plan to make full use of this.
Combat, and damage, are remarkably simplified in Shadowrun, both to the benefit and detriment of the system. More rolls are used, but they're basically identical to the opposed quick contests of GURPS (attack and defense rolls, rolls to absorb incoming damage, etc). Having flat damage values on guns and no wounding modifiers makes taking a hit require far less calculation to determine the actual effects.
Another place I prefer GURPS to Shadowrun, particularly for a system where your average gun does as much damage as most people have HP, is negative HP. In GURPS, you get at least -1xHP before you start rolling to not die. Shadowrun, along with D&D, Call of Cthulu, and a great many other systems, have you drop dead not far beyond the level where you fall unconscious. 9 damage may knock you on your ass, and 10 may kill you outright if you don't have much constitution. Even the most durable character normally available without added death resistance (dwarf or troll with max body of 8), gets 12 damage before they go unconscious, and 20 before they die. GURPS, meanwhile, if you make your rolls (aided by certain advantages and disadvantages), it's theoretically possible to keep breathing all the way to -5x HP for most people, or even to -10x for the unkillable!
One of the places that Shadowrun beats out GURPS is the initiative pass system. GURPS generally doesn't give you more than one action per 1 second turn, unless you purchase Altered Time rate to go faster (generally with substantial limitations in order to afford it). If you have purchased altered time rate, you get two actions on your portion of the 1 second turn. In Shadowrun, your speed is related to the initiative attribute, and divided into initiative passes. Everyone gets their action during a combat round, and then characters who are fast enough get to go again once everyone still standing has gone. This continues until nobody has enough initiative left for another initiative pass. I like the way this works enough that it's a house rule of mine, should anyone ever take Altered Time Rate; you act at your normal place based on base speed, then again when the round gets to Base Speed divided by actions (example, you go at base speed and 1/2 base speed with ATR 1, Base Speed, 2/3 Base Speed, and 1/3 Base Speed at ATR 2, etc). This accounts for it still taking time to actually perform actions, to prevent a character with exceptional speed and time rate from using their lighting speed and numerous actions to defeat any threats before they can act.
Shadowrun 4e and 5e have their own differences. Several key things required for the game are missing entirely in 5e, such as Autosofts needed for drones. The autosofts are listed, and how they work, but despite being listed as something that must be purchased and installed (as per most programs), no prices are given anywhere that my entire gaming group has been able to find. Speeds for vehicles have been converted to an arbitrary scale, which is handy for convenience in the Chase Rules, but doesn't tell you how fast you're actually going. There's essentially nothing given for vehicle customization in the 5e base book, including things that a runner is DEFINITELY going to want to try to keep the heat off their tail.
To be fair, 5e Shadowrun has been out for just over a year, in which time some updates and fixes may have come out that I haven't checked for.
At some point I need to run a GURPS Shadowrunish game.