Personally, if it has a split ring, I don't bother tying a loop and instead use a uni knot. I find the split ring gives the lure enough freedom of movement that an extra loop of mono doesn't make a massive difference.
However, if the ring is cruddy, I'll ditch it. Keeping in mind that with small lures, it may seriously effect the weighting and not let them dive as steep, as early, or to their full potential depth.
Horses for courses though, if you want or require that extra freedom for a certain style of fishing, by all means ditch the ring and tie a loop knot right to the t