There is no "best" aircraft in the game.
While the Comet 1 (and 1A and 2...) are bad I still got some because I want Comet 4. That's also why I got Comet 3 - they are decent for a while. Key in this game but especially in Jet Age is to decide when to dump which aicraft variant.
To the aircraft you named:
Is the B-377 bad or "worst performing"? No. If you have lots of demand in the up to 2000nm range, like the big European and some Asian Airports have, it's a very good aircraft - even as standard one. Flying it mid-range doesn't make the speed a problem as well as negates the turn around time and it can seat more people than a DC-6 or Constellation. However, even on techstoup routes it can make good money, especially if you go for uncontested routes.
The only downside is the production line is closed at gameworld start.
The DC-7 are a also a decent long-range aircraft. They can seat a few more people than the Constellation, are faster and burn less a bit less fuel. The DC-7 and DC-7B are a nice aircraft for ranges up to their absolute maximum range. The downsides are the high price and the late availability. The reason not to take them are especially the fact people already got Constellations or DC-6 and a third fleetgroup for the same duty doesn't make much sense for most.
However, Constellations (4th pilot, huge speed and maintenance as well as order costs) and DC-6B (no used availablity, slow, filled up line until year 2000) have several downsides, too, and even comparing them both doesn't lead to a conclusion one of them is "better". I ran airlines with 300+ DC-6(B ) and now I have one with, soon, 200+ Constellations. You want to use them for slightly different duties as far as possible.
Saying aircraft XY is bad without facts or aircraft AB is good without facts doesn't help and is, mostly, wrong. So yes, michele, you missed some points here...
PS: You use DC-4 and Martin 4-0-4 to their maximum range. That is wrong usage and it is why you get slapped hard by me and even alpha on this route: http://www.airwaysim.com/game/Routes/Planning/X/KLAX/MMMX/