- I've been using MediaMonkey (MM) for about 10 years to create and maintain a collection that's now over 325k tracks, stored in a mix of formats - mostly FLAC and 320k CBR .mp3. MM can do exactly what you're looking for (and a lot more, depending on the device). I use MM to sync with a 160gb iPod Classic, because Apple is the only portable device that fully integrates with my car's audio system within the digital domain.
You start by creating Device Profiles in MM for each of your portable devices, since different transcoding rules (MM calls it 'Auto-Conversion') may be needed based on the file formats playable by that device, the quality you want, and the storage space available.
Device Profiles can also specify 'Auto-Sync' criteria, which run automatically whenever you connect that device. You can choose what music and playlists should appear on your portable, and which tracks should be removed from the portable device upon subsequent syncs. Options include syncing a random subset of music up to device capacity, syncing only music from certain playlists, or syncing any subset of your library based on file locations, albums, artists, or other criteria. For example, you may want to sync all content you've rated as 4 or 5 stars; new content you've recently added to your library; the latest version of a podcast; etc. And with playlists, you can do even more powerful things. For example, I use playlists such as "sync all tracks from this artist's 15 albums, but eliminate duplicate tracks appearing on multiple albums and shuffle the rest into a random order."
In addition to recurring Auto-Syncs, you can use the same features to specify criteria "on the fly" for a one-time sync.
You didn't mention which portable device(s) you have, but here are a couple more Apple-specific items: First, MM has built-in drivers for most common devices. For most Apple devices, there's no requirement to even have iTunes installed (I hate iTunes, so that's fine by me!) Second, MM is fairly unique in also allowing you to upload files *from* an iPod, iPad, etc. to your MM host computer. You can't even do this with iTunes, but it's a great feature if, for example, you added some new content to the portable from another source, and that content doesn't yet exist on the MM host. Just click and drag, and it's uploaded.
I've talked only about syncing to portable devices, because that's the focus of this forum. But you asked about music *management* software, which is a huge topic in itself. In short, I've never found another product that can more quickly and easily tag and organize a music library into any physical structure you might desire. Extending MM's built-in functionality are scores of user-created plugins - for example, one that I use constantly has 253 (!) predefined functions able to perform almost any kind of tag editing you could ever imagine.
Last but not least, MM is one of the few products I've discovered that can easily manage music libraries of any size - it's just as fast and easy to work with 300k+ tracks as it is with 300.
Hope this helps! (Standard disclaimer applies: I have no connection with the MM developer, Ventis Media, other than as a very satisfied user.)