Supreme Sum String

Perl 6, 34 bytes

*.words.max(*.encode('utf16').sum)

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R, 77 69 59 58 56 44 bytes

A group effort now.

'^'=mapply
sort(-sum^utf8ToInt^scan(,""))[1]

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Convert to code points, sum each word, negate, (stably) sort, return first element.

Technically the return value is a "named vector" whose value is the sum and name is the winning word, but this seems to follow the rules. If you want to return the winning word as a string, you'd have to spend 7 more bytes and wrap the above in names().

05AB1E, 8 bytes

ð¡RΣÇO}θ

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Explanation

ð¡          # split input on spaces
  R         # reverse the resulting list
   Σ  }     # sort by
    ÇO      # sum of character codes
       θ    # take the last