I used to go for insulated female connectors on the + side of the battery and males on the -ve side. The reason is to avoid the risk of accidental reverse polarity connections damaging the ESC. With this arrangement it is possible to plug the battery into itself, so the fly leads are cut to a length so that they cannot physically connect together. Now I tend to use a dual conductor connector such as the Deans T plug with females on the power source side and males on the load.
In most model setups, plugs are twins - from the battery, one lead going to a two pole line socket that is polarised so it can't be connected in reverse (unless it was wired that way by the user). Similarly with the ESC power plug. ESC outputs and motor leads are often bullet connectors on separate leads to make life easier when it is discovered that the motor is turning the wrong way. Most batteries came with a Tamiya connector, nowadays a greater choice of better ones is available ready fitted. Care is obviously needed if changing from Tamiya to something better to ensure that the right wire goes to the right pin.
Red for positive with black for negative is almost universal. Having blue and yellow for the motor output leads is nice - ESC makers who insist on using red and black for their motor leads deserve to be roundly cursed.
SLA are a case where great care is needed - it is very easy to get the pos and neg reversed as they are almost identical tags, the only indication being the red dot by the pos terminal, which might have a symbol moulded in nearby.