Survival Swain. Swain isnt an assassin at all , i usually play him as a semi-tank and this is the build which works best.
Damage Swain. The first build has high dmg , but with this other you can deal TONS OF DAMAGE and pwn ur enemy's ***.

For runes as a dps i use flat ap glyphs , magis penetration marks and magic resist seals.
As a tank , i usually take armor , magic resist and a bit of magic penetration but it would be nice to take a bit of AP

I main swain since he was out , and i have tried lots of builds , and the builds which i have chosen are the best

Take W at lvl 1 , Q at lvl 2 and then take R>E>W>Q

AS a dps take classic spells: flash and ignite
As a tank i like exhaust to slow when gank or when chasing