If by best of both you mean between RAID and Core Storage then there may be some confusion as to what you want Core Storage for.
The main reason you would want to combine two disks into one with Core Storage, is if one is an SSD and one is an HDD, as this will create a Fusion Drive (where common data is moved to the SSD to give you a speed boost), but this won't do anything for you if both disks are SSDs, actually it will most likely just increase wear on one of the drives. If this isn't the case then joining two drives is concatenation, in which case data is written to one disk until it fills, then spills over onto the second, third and so-on. This gives you plenty of capacity, but has no speed benefits, while giving you the same vulnerability to disk failure as a RAID-0 (if one disk fails, you lose the set); while technically it's easier to recover data on a concatenated set, it's not something you want to rely on.
So when it comes to combining disks then RAID is really what you want. RAID-0 to split data evenly between the disks, resulting in level wear, double the capacity and potentially double speed for large files (smaller files won't see much benefit), but at the risk of data loss if one drive files. Or you can do a RAID-1, which copies data onto both disks so a disk failure won't lose anything but you won't increase capacity. In theory you should also improve performance as there are still two drives to load data from, but I've never seriously used RAID-1 with AppleRAID, so I don't know if it gives any acceleration.
However, once you've created your AppleRAID you can still convert it to a Core Storage volume, which will allow you to encrypt it (or possibly more if Apple ever adds more features). I only really mentioned it though because some of the Core Storage tools don't work with AppleRAID, in particular I was never able to convert an existing AppleRAID with a file system on it to Core Storage like you can with a single disk, but you can create a new Core Storage volume from an AppleRAID (wiping it in the process) just fine, so it's worth considering at the start for this reason.
Since both RAID types expect identical members (disks or partitions) you need to consider where your Recovery HD will go. If you're fine just creating an OS X installer USB stick then you can do that and forget about it, but if you want an internal one then what you can do is actually put one on each drive in the array (so if one fails, you still have a Recovery HD). The basic steps to do this would be:
- First of all you'll want to create an install disk on a USB stick, external drive etc.
- Install OS X normally one of your drive (let's call it A). This will create a Recovery HD and a main system partition.
- You want to clone the structure of A onto the other drive (call it B), either by creating the same partition structure or just cloning the whole drive, the latter is easier but will copy stuff you don't need.
- Booting up from the installer disk you created, you'll now take the largest partitions of A and B and combine them into a RAID-0 or RAID-1, depending upon your choice of performance + capacity vs redundancy.
- Once this done you convert the new AppleRAID device to a Core Storage volume (though you'll probably need to use the command line to do this).
I know these steps aren't very specific, I can try to find more specific commands, but I don't have spare volumes lying around so I can't completely confirm they would work.
