Sometimes the things that work with my voice surprise me. Prior to working on my singing the idea that I could cover Paul McCartney would be laughable. It turns out that McCartney or his protoge Pete Hamm from Badfinger are perfect and natural for my voice. What helps is that Paul (and probably Pete...at least it seemed like it in one interview I saw) are natural baritones (or at least they sound like that to me). These are really the easiest songs for me to sing consistently and I find all the little turns and cool things both singers do up higher to be really easy.
Where I struggle sometimes is with songs by blues singers like Kim Wilson ( a great singer) or others like him when they have a big, full, clear tone in a lower register going up to or just slightly above what would typically be passagio for me. It seems to take more effort and some days I get close...but other days I just hate the sound of my voice. Blues is great because there is typically not a need to nail the song as a cover, so I shift things and often will tend to sing a lot of lower register blues songs in a timbre and register of say Paul Rodgers. Even though this sometimes takes things up an octave, it is easier for me to do and feels more comfortable and less forced.
Part of the issue is that I have spent a lot of time over the last year or so working on the area of my voice from my passagio upwards. I need to work on my lower register probably. I can sing lower (typically have been classified as a baritone), it just isn't always comfortable or a first choice. The tone is getting better I have to say...it just isn't what I want much of the time.
Mark