"Serious ones" would probably be the most succinct.
Something that is supported by evidence or is at least both logically sound and
consistent would be absolutely fabulous.
I recommend using the link I provided in post 14 as a jumping off point for further research.
of the reasonable doubts podcast might also have some food for thought as well.
And if you want to invest a little more time into the matter, you could also try this book
by Bart Ehrman (interview here