I completely agree - Lylix is the top-of-the-crop in hosting providers for PBXIAF. We have been with them for almost three years, and their service and support has been simply stellar the entire time. It has probably been over a year since we even had to concern ourselves with support incidents with them because there simply arent any problems to deal with. Just the way I like it.
I also highly reccomend voip.ms as your trunking provider. They dont try and be all things to all poeple, they dont do hosting and their service has been so rock solid I can't even remember the last time I had to have a tech support incident with them. Their front line support is responsive, but could be more empowered to fix things - but when escalated, problems get fixed, and very very quickly.
I can not reccomend Aretta - they have stated that their trunking offers are primarily for use with their hosted solution, and that only minimal (read "poor") tech support is available for trunks used with PBX's not hosted by them.