LOR's from residents are not really looked upon as highly as letters from attendings. Residents haven't had as much experience with students and they haven't written as many letters as experienced attendings. When applying for residency, we were always cautioned to NOT submit a LOR from a resident. It's nothing personal, but compared to an experienced attending, who knows how to craft a letter and include all the "buzzwords" that will make you stand out as someone schools should really consider..., well, residents just aren't that good.
My $0.02.