Honestly I wouldn't put my money on Sweeping Strikes, it takes very long to set up a proper SS>WW combo and unless you are rocking a very strong (for your level) 2-hander I would often just prefer to WW and Cleave.
Sweeping Strikes gives you 5 extra attacks for just 30 rage I think thats amazing. If you want to activate both SS and Whirlwind you need 55 rage. If you want to use WW and Cleave you need 45 rage, but it does way less damage. You can only really compare it if you add another Cleave or WW to it.
You get 15 rage through Charge and 10 rage through Bloodrage. And you have your first weapon swing right after Charge as well. So that alone should get you over 30 rage to enable SS. WW should be ready to use after your second weapon swing. So after roughly 3 to 4 seconds into the fight. Thats not too bad.
Also you have to keep in mind that if you use Overpower when SS is enabled and it crits, your extra attack does roughly the same damage on the other mob as well.
And SS does not consume your auto attacks, like it is the case with Cleave. Cleave only gives you 1 extra attack on the other mob, consumes an auto attack and costs only 10 rage less than SS.
Here is a damage comparison I just did on the warrior I rerolled on Kronos 2. I edited out all my weapon swings to show only the damage caused by abilities I actually spent rage on. In both cases I fought 2 enemies
Sweeping Strikes and Whirlwind
You gain Sweeping Strikes.
You gain Berserker Stance.
Your Whirlwind hits Starving Buzzard for 215.
Your Sweeping Strikes hits Ridge Stalker for 207.
Your Whirlwind hits Starving Buzzard for 203.
Your Sweeping Strikes hits Ridge Stalker for 211.
Your Sweeping Strikes hits Ridge Stalker for 159.
Your Sweeping Strikes hits Ridge Stalker for 145.
Your Sweeping Strikes hits Ridge Stalker for 155.
Sweeping Strikes fades from you.
That is 1295 damage for 55 rage.
For that amount of rage you could do one WW and Cleave. I added another cleave though as WW had still a 6 second CD.
Your Whirlwind hits Starving Buzzard for 205.
Your Whirlwind hits Ridge Stalker for 212.
Your Cleave hits Starving Buzzard for 193.
Your Cleave hits Ridge Stalker for 210.
Your Cleave hits Starving Buzzard for 201.
Your Cleave hits Ridge Stalker for 199.
That is 1220 for 65 rage.
So with SS and Cleave get less damage for more rage. And you have to take into account that Cleave consumed two of my auto attacks in this case as well. In my opinion it's always worth to wait for the 55 rage to enable both SS and WW.