thanks for the replies guys.
Im in Dallas TX so mostly good roads .
where I work the dress code is casual and there is a gym right next door where I can shower so I don't anticipate having to lug a lot. Im thinking just a back pack should suffice.
I have no plans to ride in wet conditions right now but that may change in the future.
I do like the idea of commuting on the mountain bike because its more comfortable and more rugged for my weight and I can go on the curbs a little bit easier so I would still like a recommendation for a free rolling 29er tire.