I would actually recommend separate ssd & hdd (there are even SSD/HDD combos that show up as 2 separate block devices on the bus) and then using bcache or LVM cache. This gives you more flexibility - you can use part of the SSD directly and part as a cache, check usage stats, tweak various settings, make the cache bugger/smaller, etc.

I've also heard some rumors about the caching algorithms in hybrid HDDs not being as good as the algorithms used by bcache & LVM cache.