For me it's a no-brainer: Jill Valentine, hands down. Resident Evil 3: Nemesis was my introduction to the series back in 1999, and as a young boy I was fascinated by her badassery and strong determination to escape Raccoon City while being hunted by this insane killer machine. However, it wasn't until many years later when I picked up the Resident Evil 1 remake that I truly began to piece her life together and get a sense of her backstory. She gets a bad rep for being boring when she's actually just avoiding panic and showing calmness in stressful situations, which is exactly the kind of characteristic a bomb disposal expert who trained with the United States Army's Delta Force unit would have. Despite that, I always found Jill to be an extremely kind-hearted character with a strong willfulness to help others and encourage them to "never give up".
I really love this scene at the 2:23 mark in the REmake, which is the one and only time that has left Jill in a shock-like state unable to move or act... The pure terror in her eyes, unable to comprehend if what she's seeing is real or a dream, because dogs like that
can't exist, can they? Man, the animation and editing in this scene is 100% top class. Not bad for 2002.
Unfortunately Jill has been mistreated by Capcom for a long time, beginning with her humiliating role as Wesker's brain controlled slave in RE5. She was out of the spotlight for a long time until she finally returned for the RE3 remake, which I was looking forward to a lot. As a huge fan of the original, the remake wasn't what I expected and sadly Jill's character was butchered beyond recognition. They turned her into a generic action heroine who lacked many of the traits that made me fall in love with the original Jill Valentine.