I have sailed on both....Conquest out of New Orleans and in January on the Triumph.
The Conquest is 110,000 tons so it is a little larger than the Triumph (although the Promenade is basically identical).
Conquest has fish and chips on Lido deck 10....Triumph does not.
If you are driving in the day before, hotels may be cheaper in Galveston than New Orleans. I know the hotels in New Orleans downtown charge ridiculous parking fees.
I am a little surprised they are the same price, as Galveston usually has a higher price for their ships.
I do like the New Orleans port better for embarkation. I can't speak to debarkation because when we sailed out of Galveston...our cruise was a 3 day cruise to nowhere...so there was no Customs at the end of the cruise.
Either way, you will have a great time.