If your eectricity use is near 50/50 between peak and offpeak hours a fixed rate of 19 pence kWh will work out cheaper than an average of 22 pence kWh for OI. The downside of an svr tariff is the price could shoot up in June compared to a 12 month fix.
WStarmer has said he will cap prices between now and June, but not seen anything offered by suppliers yet