When I was younger, I used a lot of echolalia and a little modified echolalia and spontaneous speech. I was more likely to speak spontaneously about things in which I had no interest, because if the topic was something of interest to me, I had likely read a number of books and magazines on it and would simply script from those.
Nowadays, I use a lot of modified echolalia (hey, at least it's modified, right?) and also a fair bit of "spontaneous" speech. I put "spontaneous" in quotation marks because it's speech that's self-generated, but that I assemble piecemeal in my head, practising every few words, first silently and then in a whisper to myself. That way, when it comes time to actually say the words aloud to another person, I can just script from my practising. So it's self-generated, but I wouldn't exactly call it properly spontaneous. Either way, it seems to work.
I've always had a very advanced vocabulary (from hyperlexia and, subsequently, a childhood spent reading instead of playing) and been able to speak well on any subject that interested me - partly because I had so much material with which to work and from which to script, and partly because if I was that interested, I cared enough to try. However, I have been known to "clutter" when I talk about a topic of interest. When I'm overwhelmed (sensorily or emotionally), though, I tend to fall silent, to the point where others have to check with me to make sure I'm okay.