depends on your needs. I never used regex before , pharo regex was my first. I used on a specific case that was quite simple. I love its simplicity and its extremely compact syntax. Perfect fit for my needs, one very happy customer :)
I think it depends on complexity of the parsing and how you like to work, if you have a simple problem and want a compact syntax, nothing can beat regex. At least taking account SmaCC and PettitParser. When I need more complex parsing with nested syntax, SmaCC made a lot more sense.