Please recommend the best Pdf To epub Converter for mini kobo reader ...

I just bought a mini Kobo Reader ( for 35 US$ .. :-) ) and really enjoy using it on the go . The problem is the epub version converted from pdf files does not look good on Kobo reader (i.e. there are lots of gaps between paragraphs...) .
The same epub file looks O.K on my PC , using the epub reader plug-in for Firefox browser !

I have so far tried several "Pdf To epub converter" such as :

_3herosoft PDF to EPUB Converter 1.1.0 Build 0222
_Xilisoft PDF to EPUB Converter 1.0.5 Build 20120522
_Majorware PDF to EPUB Converter v3.1.0.0
_Calibre 0.9.36 ( freeware)

Calibre produced the best error-free conversion which still showed imperfect format in mini Kobo reader ( i.e. random gaps !! ).

My questions are :

1) Is there a way to improve the version by Calibre ? ( get rid of unwanted random spaces shown in mini Kobo reader )

2) Is there a "Pdf To epub converter " that is best compatible with mini Kobo reader ?