What ultimately matters in November is not how enthusiastic the votes are, but how many. I personally don't think adding Cruz to the ticket will do much for Trump's perceived negatives with the general electorate. You'd energize a few conservatives who likely would have voted for Trump anyway.
Jan Brewer would be a smart pick. Tough on immigration, and likely would help with female swing voters.
But I might bring five more voters if I have gusto...
Also has a strong pro-life record and A+ NRA rating.