Utilities in a namespace or in a class?

So far, if I need some commonly used utility functions, I have moved them into the utility class. Thus:

#pragma once

class QDate;
class QDateEdit;
class QDialog;
class QWidget;

class GuiUtils final
{
public:
    static void moveDialog( QDialog* aDialog, const int aMargin = 4 );
    static void setMainWidget( QWidget* aParent, QWidget* aChild, const int aMargin = 0 );

    static void setValueBlocked( QDateEdit* aDateEdit, const QDate& aDate );

private:
    GuiUtils();
};

class DateUtils final
{
public:
    static QDate today();
    static QDate yesterday();
    static QDate firstDayOfWeek();
    static QDate firstDayOfMonth();
    static QDate firstDayOfQuarter();
    static QDate firstDayOfYear();

    static int quarter( const QDate& aDate );
    static int quarter( const int aMonth );

private:
    DateUtils();
};

      

        
        
        
      

    

But I know there is another option for that. I could move all my functions to namespaces. Thus:

#pragma once

class QDate;
class QDateEdit;
class QDialog;
class QWidget;

namespace gui_utils
{
    void moveDialog( QDialog* aDialog, const int aMargin = 4 );
    void setMainWidget( QWidget* aParent, QWidget* aChild, const int aMargin = 0 );

    void setValueBlocked( QDateEdit* aDateEdit, const QDate& aDate );
};

namespace date_utils
{
    QDate today();
    QDate yesterday();
    QDate firstDayOfWeek();
    QDate firstDayOfMonth();
    QDate firstDayOfQuarter();
    QDate firstDayOfYear();

    int quarter( const QDate& aDate );
    int quarter( const int aMonth );
};

      

        
        
        
      

    

To me this seems like a better solution for creating a utility class than a namespace. I see that I need to enter more, but if I need to define a new namespace for all function groups of functions, this will be a little extreme for me. I usually don't create new namespaces other than classes, so I use the first option.

But now I would like to know that:

• Is there any advantage of using a namespace for this purpose?
• does it have better performance for using namespaces for this purpose?
• does he fit better in terms C++
  
  ?
• Is there any other reason for using namespaces for this?

I would like to know your opinion, but I need an explanation. I don't want to rewrite my existing codes and write new ones with a different style "just because". I need some kind of language / performance explanation or any other explanation as to why to use it in one way or another.

Thanks for the help.