Cruz is the more sane choice for intellectual conservatives. He’s a brilliant attorney and statesman, and has contributed more to conservatism than any other Republican in the race.
On the other hand, Trump has a tremendous moxie and appeal to people that are otherwise politically apathetic, or who wouldn’t typically vote for a Republican. He’s a populist with mass appeal, and his positions are not typical conservative ones, such as his positions on Planned Parenthood funding, taxing the highest earners, toeva marriage, and other issues.
If Cruz were to campaign on a more heavy-handed immigration policy, he’d be ideal.