1. Cooling- the tower will run cooler
2. Space in case- More room in tower for more components.
3. Cheaper- Tower case is much cheaper then a rackmount case
4. Moatherboards- More choices not limited on what type of motherboard to use.
Con's
1. Space- Rackmount takes less space.
2. Colo- Not alot of colo's will host a tower.
3. Cost- Yes cheaper to build but some colo's may charge more to host it because of space it takes.
I personally would use rackmount if you plan on putting it in on datacenter. What if you need another unit it should be cheaper for you to colo more rackmounts then towers.