Best sounding letters?

Hey, im wondering, which letters sound best, if repeated 2 times. (same letters)

Example: aa,bb,cc,dd,ee,ff,gg,hh,ii,jj,kk,ll,mm,nn,
oo,pp,qq,rr,ss,tt,uu,vv,ww,xx,yy,zz

That were all examples

Its just a "Really" off-topic question, but im from germany, and im wondered about this today, as the whole english language is about the "pronunciation"

Thank you

 

I would say ''tt''

what do you think?

 

Hm, tt sounds like ..

 

I think OO is best.

 

Some letters with sounds are "o", "A","S","E"...

 

I think uu is best as in vacuum.