Belles 21A upgrade

I haven't rolled the tubes yet since I hear the unit comes with Mullards. Which tubes are better 5814A or 12AU7? Any recommendations for the system listed below will be welcomed:

21A Belles tube Pre
Belles 150A Ref
Rega Apollo
MI2 Biwire Goertz
AQ Columbia IC
Vandersteen 2 Ce Sig II

Thanks,
Wig

the mullards were too rolled off at the extremes for me.
the tubes i like best are raytheon 5814a(great),raytheon 12au7(great),
brimar 13d5(great), cbs/hytron 5814wa(great), rca 5814.
for a smoother sound any of the conn or baldwin organ 12au7.

Do you have a source where I can order these tubes? Man too many choices?

Wig

I have a pair of Phillips Jan 5418A never used, are they better than the stock Mullards if the unit comes with Mullards?

Wig

the stock tubes in the belles 21a are mullard cv-4003 i believe.
here is a link to thread discussing tube dealers.
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1239836974&read&keyw&zztube=dealers