SnS revolve around Element or Status, so the more of either, the better. Don't neglect raw though, because you will not always have the reach to get to a monster's elemental weakspot.
Basically, here's a list of the best elemental/status Sns:
Fire: Bone Kris -> Bone Kris+ -> Bone Tomahawk -> Bone Tomahawk+ -> Qurupeco Chopper -> Djinn ----> Golden Radius. Megiddo Edge is also good, but unavailable until the final G-Rank quests. Fire is pretty rare on SnS.
Water: Sea Striker ----> Arken Duelcalion. Odyssey Blade has superior element but slightly lower raw, but requires Awakening, which is, like the weapon itself, unavailable until G-Rank. Bone Kris -> Bone Kris+ -> Ludroth's Nail -> Royal Claw ----> Harmetristesse is a good alternative if you don't like farming (Goldbeard) Ceadeus.
Thunder: This one's a little more difficult. There are 5 end-game Thunder SnS. The only Low-Rank Thunder SnS is Bone Kris -> Bone Kris+ -> Bone Tomahawk -> Bone Tomahawk+ -> Lagia Sword ----> Neodignis Whitebolt. Neodignis Whitebolt can be upgraded to Nether Lifesword or Nether Maestral; the former has slightly less raw and element than the latter, but is slightly easier to get. Hunter's Knife -> Soldier's Dagger -> Commander's Dagger -> Hypnos Knife -> Azi Dahaka -> Azi Dahaka+ -> Usurper's Firebolt (yes, it's Thunder element) -> Despot's Crookbolt -> Oppressor's Bounty has a lot of element, but is a little lacking in Raw. Sanctioned Sword has even more element, but has also even less raw. Finally, there is Qurupeco's Flight -> Qurupeco's Blight, which is unavailable until early G-Rank. It's better than the High Rank versions of the aforementioned weapons, but inferior to their fully upgraded versions. Personally, I prefer the Nether Lifesword (haven't had the time to farm for Nether Maetral yet), because it's the most balanced of them all.
Ice: apparently, Capcom hates the cold, so MH3U has few good Ice weapons. The only 2 good late-game Ice weapons are Hunter's Knife -> Hunter's Knife+ -> Hunter's Dagger -> Assassin's Dagger -> Icicle Spike ---> Nardebosche -> Nardebosche+ ----> Gran Bhavani. And Tusk Gear ----> Chalcomatia, which requires Awakening though. Both lack very high element, but they have good raw. Only the former is available before G-Rank. And oh, ya, there's the Secta Nulo -> Secta Una ---> Secta Du (W), but you shouldn't get this one unless you are very, very, very, and I'm talking VERY desperate for 3 Slots on your weapon.
Dragon: there are 3 good late-game weapons with Dragon Element. Worn Sword ---> Divine Insodus has a truly ridiculous amount of Dragon (700), but like no raw at all. Jhen Kodachi ---> Earthsbane Gladiolus has very good raw, but mediocre element. Finally, there is Alatreon Sword ---> Altheos Zodiarch, which has good raw and good element. The Altheos Zodiarch is the best of the 3, but by far the most difficult to get. Oh, and if you happen to stumble upon a Rusted Sword before G-Rank, feel free to upgrade it. It's decent enough, though like it's Ancient counterpart, has low raw and high element.
Ugh, too much time spend here. Maybe I'll post the best status weapons here later, but for now, this will have to do.