No real reason to change unless the fees are way too high. 1&1 probaly uses a third party anyway. Sometimes cheap domain name registrars charge a transfer fee that offsets the savings the first year or two. 1&1 is a good hosting company, why not use them.
BTW What is your link to hostmaster. From what I see at 'hostmaster dot com' it is only a clearinghouse or a search page not an actual company.
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