All three aircraft - Boston (both DB-7 and A-20 types), Maryland, and Baltimore were in fairly heavy use in the Med at the same time, though a bit overlapping as Maryland was gradually phased out as a bomber in favor of the Baltimore. The Baltimore and Boston were both fairly heavily modified, especially in terms of armament, though capabilities were similar as level bombers. The Mitchel / B-25 came in to action fairly late in the game, as did the B-17 and B-24 heavy bombers.
Their other main competition on the Allied side was the Blenheim, which was largely phased out pretty early on.
Here are some facts I know:
Boston was quite fast (up to 310 mph in some configurations, more in the later war versions but those were too late for action in the med). I think (only based on anecdotal comments by pilots) it was the fastest of the three down near sea-level, but not by much.
Boston / A-20 was used quite effectively in the anti-shipping role in the Med with mast-height bombing techniques and sunk some ships close to shore.
Some versions of the Boston were more heavily armed with nose guns (often added in the field) for use as low-level 'strafers', though due to effective German AAA, they took heavy losses and this strafing strategy was somewhat curtailed as compared to the Pacific. It was also used in Maritime strikes to supress flak on the ships.
Boston was considered a bit cramped by crew, as were the Maryland and Baltimore, but the narrow fuselage also contributed to their speed.
They trained in Bostons as a night fighter but I don't know if it was ever used as such in the MTO.
Had a moderately high loss rate. It was not unusual if you read through the raids in MAW that they would lose 1 or 2 on a raid of 10-20 bombers.
Had somewhat short range (~900 miles).
Maryland was quite fast (up to about 300 mph) with a pretty good 'typical' cruise speed (over 250 mph)
Was considered agile and even used as a fighter against enemy maritime aircraft (had 4 forward firing .303 guns). There was at least
one ace who scored at least five victories flying Marylands (mostly against enemy sea planes etc.). The same guy also flew the recon missions prior to the famous Taranto raid in his Maryland.
Seemed to carry a lighter bomb load in practice than the Baltimore or the Boston (often only carrying 2 bombs).
Was lightly armed and (so far as I know) never up-gunned (defense was from Vickers K guns).
Pretty good range (~1200 mile).
Had a moderate loss rate which became higher until it was phased out for over-land strikes.
Ended up being used in the maritime and high speed recon role after being supplanted as a bomber over the intensively contested land war.
Baltimore was quite fast (305 mph) but had a lower cruise speed than the Maryland.
Also had an exceptional dive speed, and was used for post-war testing of supersonic flight rather amazingly.
It was very difficult / tricky to takeoff requiring perfect coordination of throttles.
Once in the air it was considered agile, almost as much as the Maryland.
Like the Maryland it had four wing mounted .303 guns, (but no nose mounted guns like the Boston).
Had a fairly high loss rate initially when used sporadically and often on unescorted missions.
Ended up with the
lowest loss rate of all bombers on the Allied side once flown in better planned (and better escorted) missions later in the war.
Fairly short range (~1,000 miles) depending on load.
Was up-gunned with dorsal .303 being replaced by a turret with two .50 cals.
Was used in bombing operations by the British until the capitulation of Italy.
All three had a fairly low bomb load, with both A-20 and Martin 187 / Baltimore carrying about 4 x 500 lb bombs on most missions, while Maryland often only carried two.
Bombing was pretty accurate though, and all three twin engined types were considered more effective against operational targets like airfields, ports, and supply dumps etc. than the fighter bombers were.
Baltimore seemed to be the best at escaping / contending with Axis fighters, and their raids usually caused substantial damage. After their raid they would go into a shallow high speed dive to escape the battle area.
Boston was the most effective strafer and maritime strike aircraft.
Maryland had the best range and seems to have been the most effective in the fighter role.
All three were basically low to medium altitude aircraft; fast, pretty agile, light bombers. Less heavily armed than the later Allied day bombers.
B-25 carried up to 6 x 500 lb bombs, and B-24 up to 16 of them, and the latter two seemed to have done the most to pulverize Axis basis, though they took significant losses, and that was after Allied air cover was at it's maximum level. So I think they proved more decisive but the Baltimore seemed to be the best suited for the higher threat environment.