Both, but very heavily by land and minimally by sea due to its' weak navy.
Athens.
Sparta had the largest area after it conquered the southern Peloponnese, while Athens had limited land in Attica, until it created an empire for 50 years of the GREEK cities in the eastern Aegean Sea littoral.
Usually they hated each other... but in times when invaders attacked Greece, they became allies and fought the invaders. Athens and Sparta would have HUGE wars between themselves when outsiders weren't attacking. They were bitter enemies as well as strong allies.
Salamis (sea) 480 BCE Plataia (land) 479 BCE Mycale (sea-land) 479 BCE Eurymedon (sea) 466 BCE Cyprus (land-sea) 450 BCE
When Athens used its navy to good effect during the 27-year Peloponnesian War, Sparta realised that it had to get the Peloponnesian league an equally strong nave to succeed. They took money from Persia to build a fleet which finally destroyed the Athenian navy and led to Athens' surrender.
A navy is not on land, so neither had the best navy.
That would be Athens
Athens.
Sparta had the largest area after it conquered the southern Peloponnese, while Athens had limited land in Attica, until it created an empire for 50 years of the GREEK cities in the eastern Aegean Sea littoral.
Sparta led the Greek coalition by land and sea. Athens provided the major sea battle contribution, and a significant component in the land battles.
The Athenian empire was stronger at sea, the alliance led by Sparta was stronger on land.
Athens was on the coast, so was open to surprise seaborne attack. Sparta was inland and could have warning of and prepare for a land attack. However there were other factors: Athens was walled, could therefore be defended by a small force, and being connected by walls to its seaport, could import food when under siege. It could also send out an expedition by sea to attack it's attacker's home city while that city's army was besieging Athens.. Sparta was unwalled and had to be defended by land battle in the open, so it depended on the army being home and strong enough to see off an attacker. Sparta also had a large serf population nearby and was vulnerable to an uprising.
sparta's staregy was to cut off the athenian food supply by destroying crops. athens' startegy was to avoid battles on land and to rely on sea power
the Mediterranean
The Peloponnesian war was Between Athens and Sparta. Sparta was jealous of Athens and hated their idea of democracy. Sparta was strong on land, Athens at sea. But in the end, Sparta won and established an Oligarchy called the 30 tyrants. But 50 years later when Sparta was still weak from fighting Athens, a kingdom to the north called Macedonia, led by Alexander the Great, conquered Sparta.
Sparta used a phalanx and Athens transported lots of troops over sea to Peloponnesus
Persians