The PAX is an excellent choice, the PA micro tube version was my first (and many others) and still favorite for recording. The PA based on the Fender Showman / Alembic F2B preamp uses a well designed gain stage and easy to use tone stack that can vary from sparkling clean to just a bit crunchy. The Underground Accelerator is a
@Sushi Box FX development and IMHO an improvement.
The Slampegg based on the B15 has a bit more grit and is favored for R&B, rock and other music seeking warmer tones. The SVT as the bigger brother is rock all the way. The sorcery is that Senor Sushi is always striving to improve his products as can be seen by the constant evolution, every month he seems to have a new product as well as several on the bench with planned improvements like the SBVT2 and the JC Emerald2. On the SBVT he wants to improve both the mid range and the ultra switch selections iirc.