I typically do 2 ravagers, FF, NS and stock lances, and one razorwing, FF, NS, SC, and Dizzies.
Razorwing are very good- but also very fragile. I have had them killed so many times by bolters. Just basic, run of the mill bolters. It also kind of depends on what your opponents look like, and what the rest of your list is.
Unless you need something to counter fliers, I'd go with the ravager. If you do need anti-air, stick with the twin DL on the razorwing then. For pure anti armor, I'd even say the void would be a good choice.