It really depends on the manufacturer's design as one company's liner-lock is more reliable than another's lockback; and vice-versa.
In general, and all things being equal, I prefer liner-locks as they are easier to open and close. Although, I tend to stay away from the topic of "self-defense carry", I find that liner locks will deploy faster and with more certainty than a lockback of similar design.
I find liner-locks, as long as they are made properly, are more secure. There are exceptions of course as Spyderco, Cold Steel, and SOG all make very good lockback designs IMO.
The only thing I do not like about a lot of liner locks is that the blades will accidentally dislodge easier since there is no resistance of a backspring as in a lock-back, or even an Axis.