Depends on the person. Sometimes it matters how many selections you have to make. Some people have a hard time typing. Some people need symbols, some people need pictures, some people even need photographs. Typing has obvious benefits in that you can say anything you can spell, rather than depending on a fixed vocabulary, but not everybody is good at it and some people are really really slow at it. If you type on a keyboard you have to come up with the whole sentence, put it together from scratch. That's pretty challenging, cognitively. Pre-made sentences or words can be easier, or be used as shortcuts in addition to your free-form typing.
A good selection of possible communication methods should be available, that's all. For some people, blissymbols would probably be the best choice. IMO they are probably of use to people who want to maximize the variety of things they can say while still minimizing the number of selections, and who are fairly good at memorizing things.