Im looking at buying one or these breeds, but not sure which one to go for like both, anybody got any tips.

Personally i would go for a bullmastiff, but that's because i'm biased, i own four of these wonderful dogs. My advice would be to go and visist breeders/owners of both of these breeds and ask lots of questions. If you wish to email me i will try and help, you are welcome to visit and see my dogs and family to get a better picture.
Also go to some shows and speak to people there.
Hope this helps.
Karen.

Paul, please continue this in your original post. Thank you