E&L better externals, decent internals, will rust
LCT, overpriced now, QC has gone down, good externals, decent internals (advantage of which is they are all standard V3 gearbox parts which are easy to replace or upgrade), won't rust.
CYMA - never owned one but good reports generally
Tokyo Marui not realistic externals as not steel, plastic handguards etc. Shoot nicely but proprietary parts.
Having owned nearly every make bar CYMA, dependent on budget, I would go for an E&L then LCT