Wilcom has a reputation of being the best for lettering. Pulse (Tajima) is also considered to be very good (what I use). Both programs have different software levels and are expensive. Editing level software may be all you need but even that is not cheap. Whatever you choose you'll want to make sure that you have training and user support. I haven't used Pulse support much and not at all lately but they are fairly good at answering questions and they do respond in a timely manner. Pulse also has an online user's group - Pulse List where you can ask questions. There is also another group:
EmbForum - Tajima DG/ML by Pulse Users Group run by Ed Levy who gives instruction (tutorials, classes) on using Pulse. I haven't used this myself but a lot of people find it very helpful.
I imagine Wilcom has this but I would check this out first before purchasing.
Does the software matter? 
