I think there is almost certainly more, probably much more, surviving good Latin from the middle ages than from the classical period. There's such an exponentially greater amount of surviving medieval Latin in general; and little bad Latin survives from the classical age. That said, there is a very wide variety in the quality of medieval Latin writing, and some of the most interesting things to read are not the most finely-crafted from a classicist's viewpoint. *In general*, and leaving aside idiosyncrasies, of which there will be more or fewer depending on the author, medieval Latin tends to be quite similar to classical Latin, except easier. There are a number of new words and a number of old words change their meanings to some extent. There are some syntactical things you don't see in classical Latin, due to a) simplification, b) the influence of Hebrew idiom from the Vulgate, c) the influence of the evolving Romance languages spoken alongside Latin. Renaissance Latin in general becomes more classical; depending on who you read, a lot of traces of medieval usage are still there too, but with hitherto-neglected classical idioms and so forth.
*In general*, though, again leaving aside the extremes of regional variation and temporarily confusing things like orthography, or the problem of specialized technical vocabularies that the classics don't have, Latin in every period is as similar or more as is English from, say, the sixteenth century to now. Going from Cicero to a medieval writer is certainly no more difficult than going from Gibbon to 21st-century English. For a beginner a great deal of medieval Latin will be easier, even if you're studying classical Latin, just as for someone learning English a contemporary newspaper will be easier to read than one of the polished classic English writers.