You can e-mail both schools and request a list of the on-campus interviewing employers (and post them here, please!). I was unable to find these on their websites. The comparison should give you an idea if the BigLaw firms value SMU's location and/or ranking above Texas Tech.
Though, for BigLaw, I'm guessing you will still need to be in roughly the same top % of the class at either school.
EDIT: And that deposit at Texas Tech should be refundable until the first week in April. If you're still unsure, just pay it for safekeeping.