You can get alot of utility out of a size 1 Active sensor even in the early game, options include a 500 HS sensor for detecting commercial ships (>25,000 tons), or perhaps a higher resolution sensor which could detect a destroyer at 10 million kilometers, or hell even resolution 1 you get a million kilometers which is great for detecting beam ships or fighters which may be sneaking up on your commerce.
Of course personally I like to equip my freghters with a resolution 16 sensor, for er, detecting FACs which might be sneaking around 'preying' on my ships.
