Guns of the top 6 candidates:
EDIT: corrected armament of the Bloch
MiG-3 - Started out with a heavy armament of 2 x LMG and 3 x HMG, this was reduced on some aircraft to save weight to 1 x HMG and 2 x LMG or even 1 and 1, but it didn't help much.
LaGG-1/3 - Also started with heavyish armament of up to 5 machine guns, ended up with 1 x hub 20mm ShVAK hub cannon and 1 or 2 x HMG or LMG. Still fairly potent by early war standards.
MS. 406 - One hub mounted Hispano 20mm cannon (60 rounds) and two LMG
Bloch 150 / 152 - Two wing-mounted Hispano 20mm cannon (60 rounds) and two or four x LMG
Fiat G.50 - Two HMG
PZL P.11 - Two to four LMG
So of those, I would say the P.11 and G.50 were the least heavily armed, though not necessarily the worst fighters of the group. The I-16 by the way, was armed with just two LMG in the Spanish Civil War but most variants that faced the Germans had 2 x 20mm ShVAK cannon plus 2 x LMGs, all in the wings. Soviet cannon were quite good, their HMG were good, their ShKAS LMGs were superb. The Breda HMG in the Fiat were considered pretty bad, slow firing and relatively lightweight ammo for the caliber.