11dpo today and just got my first vvvfl. I think it's not a great idea to compare different tests. Even using the same test could cause unnecessary stress as maybe you urine is too diluted. I'm going to test again on Sunday or Monday hopeful for good line progression.
I only ever used First Response, but I don't think that pregnancy tests are the best way to determine your hCG levels. There are at-home blood tests but I'm not sure how much those cost. Maybe you could try those tests that estimate how far along you are and see if that progresses?