Personally I would place reliability above all else.
Recently I had the slowest entry-level SSD and was impressed with results over HDD. Then it crapped. So I bought the most reliable. They are currently on sale. Straightforward 128 GB would probably be faster than 2x 64GB in RAID since 128 is essentially 2x64 worth of chips in a raid-like array anyway. But yea, if you do find 2 64s with same specs, but still, everyone [else, much more knowledgeable] is going to ask what you are trying do, so you might want to expand your OP if you want "other ideas".