Which group elements have the most metallic character?

Elements with lower ionisation enthalpy are said to have more electropositive character (metallic character). Metallic character is defined by the tendency of losing electron(s), to form cations.

Group 1 elements (Alkali metals) have one electron in their valence shell. To attain noble gas configuration, they readily lose the one valence electron. Therefore, they have the lowest ionisation enthalpy and hence the highest electropositive character.

Other metals have multiple electrons in valence shell, and removal of the valence electrons in those cases is energetically not favourable (ie, it requires high energy to remove electrons from such atoms).

As you might know, the metallic character increases down a group, and decreases across a period.