The Hall's have an onsite compressor, self use, single filtered (?) and sometimes a bit low on pressure. No Nitrox, unless its changed recently. Sovereign have clean and Nitrox, although make sure you collect and analyse in the evening as it gets a bit tense if you try that in the morning.
Prefer the Hall's skipper, nice old boy. Sovereign have good food and accom on site. At the Hall's place the local pub does pretty good evening food. Be aware the Hall's have a meat eaters attitude to veggies though
at breakfast time.
Beware of the local pubs near the Sovereign base, (The Ship?) not the best food selection/choice or size of portions. I walked out as the service was so bad.
HTH
Matt