GLP or RoA On swain?

That's depending on the game. In general: If you are ahead and have enough gold, go GLP, if behind go RoA. Also consider the usefulness of the slow against your lane opponent.

I think that GLP synergizes very well with his kit. The slow active helps you land W, the mana/health and health/mana regen are very good with his ult... And all Swain players that I've seen recently always build GLP over RoA. Also, some more damage on a 40s cd isn't bad for a mage.

Comment.

RoA forever and always

I wish GLP's active was more satisfying, because I would totally go GLP if it were.

I dabbled with it when it first came out, but what I found was that the way the active fires made it too hard to use effectively to be useful with Swain's kit. I find his Q to be a sufficient slow, and GLP isn't really necessary. That being the case, I prefer the extra stats.

In a better world, GLP would be more useful and RoA wouldn't be mostly a ball of stats. We're not in that world yet, though.

If I see a Swain build GLP I know he's bad or never played Swain before.

I like ROA. Lets you survive better

I prefer GLP to make landing snares easier. The deciding factor in most trades and fights is whether or not you land your snare. If you don't you will lose and if you do you will win. The gained slow active more than makes up for the loss of stats.