Both of Wind Ranger`s facets are strong, but in most games, you`ll want to take the Whirlwind facet. Your facet choice may have some small impact on your item build, but not a massive one, so I`ve decided to keep the build unified here.

Let`s consider the relative strengths of Focus Fire vs. Whirlwind. I`ve had to make some reasonable assumptions about item timings for the Focus Fire side of this, but it`s not going to swing much even if you change those assumptions a bit. Whirlwind attacks at a fixed rate regardless of your item build. Focus Fire adds a large amount of bonus attack speed on top of your item build, but even avoiding attack speed items, you`re going to exceed the 700 attack speed cap in the late game.

Equivalent total attack speed
||| Focus Fire | Whirlwind
1 | 489 | 263
2 | 582 | 342
3 | 678 | 422

Attacks/second
||| Focus Fire | Whirlwind
1 | 3.22 | 1.75 | +84% for FF
2 | 3.84 | 2.25 | +71% for FF
3 | 4.55 | 2.75 | +65% for FF

Of course, this is only looking at a single target. As soon as you`re hitting two or more targets, Whirlwind is doing more total damage at every rank. Focus Fire is always going to be better for killing a single target as quickly as possible, but Whirlwind is still reasonably good against single targets. One big advantage for Whirlwind is that it doubles as a very strong farming tool, allowing you to rapidly clear Ancient stacks that you`d be unable to take with Focus Fire; this can make a significant difference in your timings and is a big part of why Whirlwind is the more common choice. The best facet really depends on the two drafts in a given game and your role in those drafts, though. If your team has multiple scaling cores, and the enemy team is a four-protect-one draft, just ensuring you kill the one every time with Focus Fire may be the best choice. If you need to be the primary scaling hero for your team, you can carry harder with Whirlwind.