PettitParser provides a more Pharo orientated syntax. SmaCC uses syntax very similar to regex. SmaCC comes with a lot of parser for programming languages.
I chose SmaCC because a) the syntax is very compact and it allows me a bird's eye view over the overall syntax definition, but also more difficult to read. PettitParse is the opposite , much easier to read but more verbose. b) It comes with a very detailed python parser and many other parsers. For less powerful parsing you can use also regex which is what both parser are based on as a general idea. The advantage of regex is that is already included inside Pharo. However if you plan to extend your syntax and grow it to something complex pettit or smacc will be a far better choice. I use smacc to parse python data types (list, dictionaries and custom python types) to pharo objects and so far has been working like a charm. I could do the same with PettitParser but having a python parser saved me time in the short and long run. I also really like the compact syntax, it took me time to get used to regex syntax but now I find quite easy to read. Hope that helps you.
