IMO Pittman is a much more dynamic player, and overall a decent starting caliber NFL HB. I would think he would be more expensive than Allen. I like him better than Gary from Denver as well, though I like Gary better than Allen.
sorry, i don't really know a lot about either one. i think they'd both rank as average-to-good backs. iirc. allen can catch out of the backfield, and i think that intrigues the texans. but ultimately, they're gonna sign the best guy at the cheapest price; i don't think either one is an answer, nor are there any answers available, just fill-in/eventual back-up types.