Personally, I prefer Phillipa. She's insanely well characterized and her voice actress is just, oh so lovely
I could go on and state why she's badass, but fuck it. It'll take several pages.
I will however add one thing: Did you know that Phillipa fights Dethmold in the background during the Siege of Vergen! In my third playthrough, I was staring in shock as I saw them fighting. They were just casting spells at each other and blinking out of the way but still. I didn't even suspect anything like that was going on during my first playthrough. Don't have any footage of it but when playing through Iorveths path, keep your eyes open and you'll see Phillipa and Dethmold fighting above the Vergen walls. It's a pretty cool detail