It depends on what I'm doing. Most of the time I use the Testors brush-on cement. For missile pylons and other things that will likely break off, I use a little CA glue ( the crystalline nature of the glue lets the parts pop apart, rather than actually break ). For canopies I use CA or white glue, depending on the situation.
I had a tube of the gel cement that went without use for years until recently. A guy asked me to build a kit of the "three soldiers" statue at the Vietnam memorial. Reluctantly, I accepted the job to help a vet ( I can't stand IP figure kits
). As expected, the parts fit terribly and the compound curves would have made puttying a nightmare. It suddenly occurred to me, why not use the gel cement? It'll go in place with minimal work and will carve easily. That little experiment paid off and I've used the technique a few times since then.
Just a little tip: don't try the "gel cement filler" technique for large filling jobs or where you're going to be restoring panel lines.