Whether to specify ddf in confint.svyglm()

Question

I have a main question about whether to specify ddf in confint.svyglm(). Using the two specifications below generate slightly different confidence intervals. Specifically, my questions are:

1. If it would be preferable to use ddf = degf(m$survey.design)?
2. A secondary question is: which method is preferable, Wald or likelihood?

Any thoughts would be greatly appreciated!

library(survey) 
data(api)

dclus2<-svydesign(id=~dnum+snum, fpc=~fpc1+fpc2, data=apiclus2)
m<-svyglm(I(comp.imp=="Yes")~stype*emer+ell, design=dclus2, family=quasibinomial)

confint(m, method="Wald", parm=c("ell","emer"), ddf = NULL )
confint(m, method="Wald", parm=c("ell","emer"), ddf = degf(m$survey.design ) )

confint(m, method="like", parm=c("ell","emer"), ddf = NULL )
confint(m, method="like", parm=c("ell","emer"), ddf = degf(m$survey.design ) )