Personally, Martha... I wouldn't hire anyone who "badmouthed" the competition. But that's just me.
Selling real estate is not rocket science... but it's also not something that's formulaic. Meaning there's just no tabulation, or logarithm that we can use to build a price. So it often comes down to the agent's familiarity with the area, their experience (how long have they been doing this, how many homes of your type in your area have they listed), etc...
So it's not uncommon for agents to come up with different valuations... and since commissions are negotiable, each agent/agency decides what they charge, to make sure that the fee covers the expenses for all of the services that they offer.
So you need to do your homework... find out the history, experience, of each of those agents... how many homes did they sell last year, last three years.... what was their list/sell ratio on those homes... what percentage of their business is listings vs. buyers... are they prominent in your area in the type of home you have to offer.... are they a full-time, or part-time agent.
Ask them to explain exactly what services they offer for their fee, and ask them to explain why they charge what they charge. If one agent is charging less, make sure that they're not just deducting that portion from the buyer's agency commission that they're offering on the MLS.