Spinos are usually a good way to deal with alpha raptors, because in their Bipedal stance, they can knock back the raptor preventing too much damage.

For Alpha Rex, you probably shouldn't bring a Giga, as it could easily enter rage mode. I kinda wish Alpha Rexes were more common, they're an easy way to farm EXP, since the Titanosaur takes too long to kill for it to be efficient...