I think how you make the bait should be based on what you want the final bait to look like. Each mentioned technique will result in a different look to the bait.
For example, if you hand pour the belly (or top) and shoot the rest of the bait, the body and tail will be the color you injected.
If you use the twinjector properly, the bait will be half and half colored with a blend between the colors where they meet and the tail will be laminated as well.
With the laminate plate, the colors will be distinctly on each side and no "mixing or blending" where the colors meet. Tail will be laminated as well if the plate goes all the way out.
I personally like the tail of the bait to have the 2 color look when I laminate on most baits however the pour the belly and inject has advantages as well.
I to adhere to the aformentioned principle of the baits not being perfectly 1/2 and 1/2. The blending of the colors gives different looks to me and no doubt fish key on things that are not ordinary in their environment or the "different" looking baitfish/food source. Of course, that is just me and the fish probably have a different opinion but I have yet to get a good response!!!

Time ends up being the last factor in most of the baits I do as once you decide on how you want the bait to look, you are move into one of the above mentioned methods or a slight variation on one of them.
In the end, they are all methods I would use based on my level of pouring/injection and the resulting bait color I was trying to make.
Jim