It's a tough question, as aircraft and thus air defences evolved considerably over the course of the war, each country adapting to the threats it faced. Looking at the UK and Germany, both had strong defences against the daylight raids they faced in 1939/40. The British Dowding System of command and control was the key to victory in the Battle of Britain, something I've [written about before] (https://www.reddit.com/r/AskHistorians/comments/80a7j9/exactly_how_did_the_use_of_radar_technology_help/duugrem/), allowing Fighter Command to efficiently deploy its resources to win the battle of attrition. The Galland quote in that piece ("From the first the British had an extraordinary advantage, never to be balanced out at any time during the whole war, which was their radar and fighter control network and organisation. It was for us a very bitter surprise. We had nothing like it.") is a little overstated; at the start of the war Germany had more, and better, anti-aircraft guns and experienced fighter pilots. Their network were not so well integrated, but faced a rather different threat of small formations of unescorted bombers operating at long range rather than massed waves just over the channel. British attempts to bomb the German fleet in daylight in 1939 resulted in unsustainable losses, resulting in Bomber Command almost entirely switching to night attacks for the rest of the war.

Until 1941 neither Britain nor Germany could do much to stop night attacks past anti-aircraft barrage fire based on sound or fighters hoping to spot something in searchlights or moonlight (in the first two months of the Blitz the Luftwaffe made 12,000 night sorties, the RAF shot down eight German aircraft at night). The British Chain Home radar was unsophisticated (though effective), facing out from the coast and no use once enemy aircraft were over land. German defensive radar development lagged somewhat, the Luftwaffe being more focused on the offense; they did have Freya early warning radars operating on shorter wavelengths than the British Chain Home systems, but not a complete network at the start of the war. Both sides lacked more precise radar for searchlights, gun-laying or directing night fighters to a target, and neither had devoted much effort towards dedicated night fighter squadrons.

The British had been developing aircraft mounted Airborne Interception (AI) before the war, but the first units were unreliable, had a short maximum and long minimum range, and were mounted in Bristol Blenheim fighters that were barely faster than the bombers they were chasing. Various, somewhat desperate, schemes including aircraft-mounted searchlights and Long Aerial Mines (dangling bombs on cables) came to naught, but by early 1941 the British had Ground Controlled Intercept (GCI) radars to get night fighters close to their target, and fast, heavily armed Bristol Beaufighters with more advanced AI Mk IV radar. Somewhat ironically the night Blitz was winding down just as the RAF were in a position to effectively challenge it.

The Luftwaffe formed its first night fighter unit in July 1940 under Josef Kammhuber, who developed what became known as the Kammhuber Line, a series of Himmelbett boxes within which fighters were directed towards bombers by radar and searchlights. German airborne radar development was slower, and lacked the cavity magnetron that allowed for compact centimetric radar, they started to deploy Lichtenstein AI sets in small numbers in 1941. Night bombing became a battle of electronic warfare - radar for detection and navigation, navigational beams (first used by Germany in the Blitz), radar detectors, chaff ("window" or Düppel), jammers, etc.

With the entry of the US into the war signalling the start of the Combined Bomber Offensive, Germany faced round-the-clock attack. Daylight raids by unescorted US heavy bombers with their heavy defensive firepower required different tactics to the careful stalking of night fighters: heavy weapons to inflict maximum damage in minimum time (cannons up to 50mm, rockets), heavily armoured Sturmböcke (battering ram) Fw 190s etc. German air defences were at their height in 1943/early 1944, both Bomber Command and the 8th Air Force suffering heavy losses that would have been difficult to sustain. The arrival of long range escort fighters in 1944, the P-38, P-47 and particularly the P-51, allowed the USAAF to take the fight to the Luftwaffe, particularly during "Big Week", February 1944, breaking the back of the Luftwaffe, Allied bomber losses decreasing from that point as relentless attrition ground down the defences.

The UK, meanwhile, had little to contend with, the majority of the Luftwaffe's offensive effort being in the east. Small-scale "tip and run" raids, the "Baedeker Blitz" of 1942, Operation Steinbock (or the "Baby Blitz") in 1944 kept defences on their toes, but were pinpricks compared to Allied efforts. Radar continued to improve on the ground and in the air, as did the night fighters on which it was mounted, most notably the de Havilland Mosquito. The most sustained attacks came from V-1 flying bombs from June 1944, about 10,000 in total launched against Britain. Of those, about 7,500 were observed by the defenders, and more than half of them were brought down by defences: the RAF's fastest fighters by day, including Meteor jets, Mosquitoes at night, and vastly improved anti-aircraft guns bolstered by the excellent US SCR-584 gun-laying radar and proximity fuses. Just by virtue of resources and technology it's hard to look past the UK's late war air defence network, but then it was powerless against the V-2 rocket, and had jet bombers like the Arado Ar 234 been available in numbers then the scales may have tipped back towards the attacker again.