Who would best balance out my team?

[KingOfClubs]

Right now, my line-up is:
Umbreon
Salamence
Mamoswine
Meganium
Rhyperior

Should my sixth be:
Blaziken
OR
Breloom?

 

[Kayke™]

Your best bet would be Blaziken, imo. You've already got a Meganium to cover grass. (Which isn't completely necessary.) Since Blaziken covers two types you probably need in your party a bit more, he seems to be the favorable one. Just my opinion though. ^^;

 

[Urablur]

Agreed with Hata-kun.
Both types cover fighting but Blaziken would be an ideal choice in relation of types.

 

[Eos Aduro]

Breloom needs Jask Support. I think your team needs a special tank, but Blaziken out of the two you have posted.