The choice between a semi-floating axle and full floating axle will depend on two things: your budget and your vehicle. If you vehicle is working into certain stress limits and you don’t use it for any heavy duty purposes, then a semi-floating axle is just fine. You would not gain much benefit for the cost to convert to a full-float axle.
On the other hand, if you regularly haul a lot of weight in the back of (or behind) your vehicle or are involved in off-roading, then you’ll want a full floating axle. It may cost more money, but it’s more durable and supports more weight.
A benefit of a full-floating axle, finnally, is that even if an axle shaft breaks, the wheel will not come off, preventing serious accidents.