So, we visited both Venetian and Tattenhall this weekend. Venetian was OK although the fact they don't permit you plugged into shoreline whilst away from your boat could be problematic for us. The marinas were very different, Venetian seemed to be somewhere you'd store your boat whereas Tattenhall was somewhere you'd like to stay with your boat - if that makes sense?
The cafe at Tattenhall is great - good breakfasts and the people were very accommodating. The marina has excellent 4G mobile network coverage which is important to us (monitoring+TV etc). Oddly its a leisure only marina, but the carparks were suspiciously full and people on most boats - maybe the leisure bit is very flexible! We've signed up for Tattenhall so looking forward to doing some northernish stuff! thanks for all the help!