Mastercoin is a sort of Bitcoin functionality extension, built on the top of existing bitcoin block chain. Their success will make bit coin more attractive - allow for trading contracts and shares etc using block chain - but would also put more stress on the block chain and miners, probably resulting in increasing its size. They are not competitors at all (except for VC funding), they have to stay on the good side of the Bitcoin Fundation, as BF can completely kill them. The Etherum is an attempt to build new infrastructure, imho they are rather competitor to Ripple, not bitcoin. I do not think that either Ripple or Etherum winning should be good or bad for bitocin. Generally, all meaningful new initiatives and cryptos like that are good for ecosystem, except that they increase competition for funding (and later investing in these cryptos).
