Playing with a pick and fingerstyle differs the sound. I believe it's better to practice both and use the one that fits the song. If you are switching from pick to fingerstlye and back again, it will be a good idea to use a processor to balance the sound when switching between styles (in general playing with a pick produce higher volume than the fingerstyle, at least for me).
Also when playing fingerstyle if you pluck nearer the bridge, you can get closer sound to pick style.
You should check your attack as well, I mean how hard you hit your fingers to the strings. And if the notes goes dead, I'd look my fretting hand as well. If you let loose your fretting fingers the notes will fade soon.
hope it helps
