LXQt

If you’d like to have a unified theme for all your GTK2/3/Openbox and Qt4/5 applications and be able to customise them:

1. Choose gtk in lxqt-config (LXQt System Settings>Appearance);
2. Install well maintained themes supporting GTK2/3 and Openbox;
3. Edit manually the theme files to further customise if you like.

For a pure Qt4/5 system you don’t have really an option to choose a preset or customise the default one. You may use the default fusion and wait either for qtcurve or for vitality (bespin developer’s new creation) to have a config tool. Or another generous soul may create a qtconfig-qt5 in the mean time.