If you're going for incentives stick to one. To me PDB is a non starter because of the hoops you have to jump through (peak hours, 90% acceptance rate etc). I personally find Uber is busier, as well as bigger Boost zones and Quests. I generally run Uber more and use Lyft for 2 things:
1. See where demand is in Boost zones. The pink squares usually indicate activity, and most of the time Uber Boosts are higher than the Lyft PT.
2. If I get taken out into the burbs, occasionally Lyft will be PT while Uber will be base.
Lyft almost always takes longer to get a ping, even in areas of alleged high demand. FedEx Field Sunday night when I was in Uber's alleged surge zone (red as a babboon's ass) I would turn on the app and get pings immediately. Since they were base rate/no surge, I did the no thanks button. Timed out within 20 seconds. Did this repeatedly. I had Lyft on as well and even though it was burning pink, no pings for minutes. Ultimately i got a nice PT ride on Lyft while Uber played games with surge.
In a nutshell, yes, but it can be very hectic to be online in both apps constantly and you may take an accidental acceptance hit (when you need to keep it high for a guarantee) if you aren't careful.
I generally do uberX exclusively in Northwest DC & Arlington. But if I get slung way out into suburbia, I'll turn on both apps with a DF set to get me back to the closest densely populated area and take whatever comes in first. Also, if I sit in NWDC/Arl for longer than 10 minutes without an uberX ping, I'll turn on lyft too. And I'll switch it up and drive lyft exclusively for the earnings period if their guarantee/bonus happens to be higher than uber's that week. You gotta chase the biggest carrot and catch it as well to be as profitable as possible.