Farsight was the more infrequently-chosen of the pair, thanks to the sharp restrictions he was burdened with; you could only use him in games of over 1500 points, and he hamstrung your ability to bring a variety of useful units, and also Vespid. Those restrictions are thankfully done away with, though it does raise the question of where the isolated Farsight Enclave is getting its four-fingered hands on XV104s and ion rifles. As a commander, Farsight is pretty well built, with a solid statline, including WS5 and I5, a good Warlord Trait (no scatter when his unit deep strikes), and the option to bring his 7-strong bodyguard team. The combination of a perfect deep strike, six bodyguards with plasma/fusion and target locks and one in support could be absolutely devastating, no matter whose backfield you're dropping into. Of course, at a minimum of 684 points (Farsight, 7 x Bodyguards with 7 x PR/FB/TL, MSS, CCN, PENchip), it had better be.
Strangely, Farsight seems to have left a slot on his commander-variant battlesuit empty, as he takes to the field with just the Dawn Blade (AP2 Armourbane), plasma rifle and shield generator. Where's your VRT, O'Shovah, or your Stims, or a second plasma rifle? Or more to the point, why is the single best challenge character in a book that otherwise has nothing to throw at close combat monsters not wearing Iridum armour standard? It seems like an oversight to me, and more it seems like something that could be justified on the table-top just as well as in the fluff. Farsight leads from the front, preferring a bold, close-in style of combat; why wouldn't the spearhead fighter wear the best armour? He's going to be taking the most firepower right in the chest, after all.
Shadowsun, in contrast, is a veritable tank on two relatively tiny legs. A 3+ save, plus a 5+ invulnerable save, plus Stealth and Shrouded, and if she brings a couple of MV52 shield drones along not only does her unit's average toughness rise to T4, but she has a couple of 3+ invulnerable saves she can pass particularly worrisome wounds off to. She also has Infiltrate, and a perfect Look Out, Sir! when she's in a squad with other stealth suits, and her Command-link drone allows a nearby unit to re-roll its To Hit rolls of 1. Oh, and she's a BS5 model with two fusion blasters that can target two different models. And her unit gets 3D6" for its Thrust move, thanks to her Warlord trait.
While Farsight is clearly designed to be the burning heart of the Farsight Bomb, it feels like Shadowsun is meant to babysit the Riptide. If she only brings the Command-link drone the three-strong unit has three different T values, meaning it sticks with the superior T6, plus the Riptide is more mobile, and it's got a constant 4+ cover save against shooting. Having Shadowsun along basically provides a slightly inferior version of two different Nova charge results at once, without having to risk rolling for the reactor in the first place. And since she's LD10, you could even bring a couple of shielded missile drones along without having to worry that the loss of one of them will send the Riptide scampering. Curiously, though, despite being the Tau character most closely associated with drones, Shadowsun does not herself come with a drone controller.
Shadowsun and Farsight can technically be fielded in the same army together, giving the Farsight Bomb Stealth and Shrouded and adding the ability to deal with yet more units. You know, just in case you weren't already reducing any clustered target to a smoking crater. If you do this, however, be prepared for anyone even passingly familiar with Tau fluff to roll their eyes at you as hard as is humanly possible. It will be the least you deserve.