Playing your own solo is easy than following somelese's solo. But to play our own very good and the best solo is harder. That means we have to improve ourselves. No matter spontaneous or work them out before playing on the real occasion, both are still considered the hardest because it is your own piece of creation. Plan or not to plan your piece, it will still be the same as the only differences is how variety can you play? If you can do spontaneous solo, but almost in every jamming session you played almost the same solo everytime. That means you gotta' plan next time in order to show variety. Same to those who plans or create their own piece ealier before jamming or live occasions, but variety must be there. So that means depends on songs and music you are soloing with and how many times you play that piece and be sure to make it at least a lil' bit different from what you have played. Why not you play spontaneously but plan your work just in case if you are facing some difficulties in following sudden chord changes, eg: What if the chords suddenly changes to this and that and etc? And say, I got off-tune to this note... Is there any way I can change this around or maybe add a few or more notes so that it won't sound so off-tune. Try to make it natural.

Hmmm... actually, all this can be compiled to and get one results... "PRACTICE MAKES PERFECT"... so either way you can be the best.