Tattier the better, to deter thieves. SS for simplicity and ease of maintenance, unless you live somewhere very hilly. I run a 38/16 combo on mine; good for acceleration at lights, and reasonable speed. Not too high when you're tired though.
Suspension unnecessary and heavy. Decent wheels, with tough commuter tyres (I use Spesh Nimbus). 1.5" a good compromise for speed and comfort.
Mudguards and a rack, to keep you a bit drier/cleaner, and to carry stuff.
Decathlon sell 5-sided 'allen key type' security skewers, or use solid axles.
Proper tough lock. No point in scrimping here, as it just means needing a new bike if you get a cheap one, as it will be broken.
Basically, a bike that's unattractive to thieves, that works well and is easy to look after.