I'd definitely take the option running from Tottenham Hale to Bishops Stortford and Hertford East on the Lea Valleys. Personally, its about time those routes (via Enfield Lock and Seven Sisters) received decent upgrades.
The line specifically from Tottenham Hale to Bishops Stortford is a candidate for four tracking, particularly as traffic grows and capacity (often restricted by the Stansted Express) continues to be stagnant.
Whether or not you would run it to Alexandra Palace is somewhat irrelevant; few gains to the cost of staging.
Preserving the right to run slow trains almost every 2 minutes, and still having fast trains to Stansted, Cambridge etc, you create the options for future growth.
I would run the route from Epping to Loughton (which would be the terminus of the Central Line), before diverging and tunneling past Chingford (interchange for the Chingford branch) and then Tottenham Hale. This part of the Network would then join in with trains from Bishops Stortford and Hertford East. So, 4 off peak trains per hour from Epping, 4 from Hertford East and 4 from Bishops Stortford. Jobs a good'n.
As for "South of Tottenham" - well, let's see.
I would tunnel down immediately: stations would be Stoke Newington, Dalston Junction, Angel, St Pancras International (Thameslink interchange), Tottenham Court Road, Green Park, South Kensington, Chelsea Kings Road and Parsons Green. From here, you can run "Crossrail" services towards Wimbledon (and onwards to other destinations), but also complete simple infrastructure improvements to use the Hounslow Loop.