I have a small fireplace measuring 25" wide 24 1/4" high and 16" deep. so far I have only found the Sierra 5300 Cricket to fit..is this a good insert? are their others that would be better?
I'm not familiar with the Sierra, but I think Jotul makes a small insert -- a gas-fired direct vent design -- that might fit. Jotul has an excellent reputation for making high quality products that are manufactured in Norway but assembled in Maine. In my experience, there was just one reservation -- their 800 # is not designed to handle "retail" issues. It's really for the contractors who install their products. So make sure you can trust the expertise and competence of your installer. But you'd want to do that any way. Installing these inserts is complicated and takes about a whole day. You really need to make sure they know what they're doing.
One more thing: when you figure out whether a particular insert will fit, you need first to make sure that it will fit into your existing firebox. That's self-evident. But you also have to make sure that the "clearances" are right -- these are the distances between the hot stuff and the combustible stuff. If your clearances are not right you might have to make some additional modifications to your fireplace surround, hearth and/or mantle. And make sure you do not have a code violation, or else your insurance will not cover you if you have a fire.
Decisions,decisions. This isn't straightforward, and it does cost. But in the end it will be worth it.