I use them when appropriate, but I've seen them fail (as you probably have). There are boxes which you cannot change unless you want to rip it out and replace with a bigger one. If the box is too small and the existing wire is crowded, wire nuts make me nervous. I'll use crimps, as long as there's enough wire to work with in case the crimp has to be cut off at a later date. For new work, I always install an oversized box so there's enough room to use wire nuts correctly.