[Nerd] My personal opinion is:
Imperium of Man vs Star Wars
Fleets:
Imperium capital ships are ancient miles long space-cathedrals each, if equipped correctly capable of wiping out the population of a planet.
Empire capital ships (excluding the Death Star) are massive fighter-wing hangers, their size, if Videogames mean anything, is probably roughly comparable to the Imperium's ships in size, however looking at Battlefleet Gothic, the Imperium's ships are, class to class, better armed. The Star Wars ships however have many more fighters. In fleet actions, the Imperium and Star Wars are probably relatively even, untill the Imperiums sheer attrition wears in.
Hardware:
Imperium, military standard issue is the "Lasgun" it is one of the weakest weapons in the setting although writings describe it as a dangerous weapon capable of causing horrific wounds.
Star Wars standard issue is a similar "blaster" another energy weapon similar in character to the Lasgun, they do range in power however the standard issue weapon seems somewhat less powerful than a Lasgun.
Imperium exotic weapons range from the Bolter line of weapons, essentially high-powered ammunition weapons capable of killing people when shot through concrete walls. To C'Tan Phase weapons, which exist on multiple planes of existance and contain parts of "Star Vampire" gods, one of whom put the fear of death into every living thing in the galaxy.
Star Wars exotic weapons again vary, if EU is used then these range from an energy rifle capable of vapourising any living target, although it takes time to charge to that level of power. To light sabres, need I say more. There is LESS horrific weaponry though.
The Imperium's military vehicles range from relatively weak Tanks and APCS (Chimeras, Salamanders, Rhinos, Razorbacks) Through to main Battle (Leman Russ, Predator-And Varients) Artillery Units (Whirlwind Tanks, Basilisks) ungodly mostrasities (Baneblade Tanks, Land Raiders-And Varients) to the Titans, titans are giant mile high humungous mecha with guns that level cities (well, kinda).
By contrast Star Wars doesnt have that much, a few Battle Tanks and Scout Vehicles. The most noteable vehicle is the AT-AT, which is probably on a Par with some of the SMALLER titans, although its armament is not that impressive and I would place it roughly on the same threat level as a Baneblade.
Armies:
The Imperium has the Imperial guard, a redshirt army that epitomises the words "We have reserves". The Imperial guard has troops that range from barely trained conscripts equipped with a flashlight and a tee-shirt (Lasgun and Flak Jacket), to highly trained professionals, some of whom are in live fire exercises before they learn to read, equipped with all manner of things. The Guard are almost without number. Also important to note is the Guard come with a large backing of artillery and armour support.
The Imperium also has the Adeptus Astartes, or Space Marines. Supersoldiers trained from childhood, often recruited from the myriad "death worlds" that the Imperium owns. Each marine is a titanic killing machine engineered through surgery and genetic tampering into a superhuman. Standard issue Astartes equipment is Ceremite Power-Armour and a Boltgun. The armour, if we go true to books and the game "inquisitor" essentially makes Astartes walking tanks who, induvidually are more than a match for an Inquisitor (who again according to books and "inquisitor" are probably roughly comparable to Jedi and all but the most powerful Sith in power). The Astartes rank and file however are the least of them, from heroes wielding ancient weapons like Power-Swords to veterans equipped with Tactical Dreadnaught (Terminator) Armour, which by defalut COMES WITH a Power-Fist... which can punch though tank armour.
Initially there were 20 Legions of 10,000 Marines each, however after 10 of these "went rogue" they are now split into chapters of ~1,000 Marines each, there have been new foundings of chapters in the 10,000 years since their inception though.
The Star Wars factions essentially have either, Clone Armies, probably on a par with some of the better Imperial Guard Regiments, but almost certainly outnumbered by them. There is no Space Marine equivalent for the Star Wars galaxy.
Special People:
The Imperiums Inquisition is chock full of (often Psychic) special ops trained warrior priests, each equipped with anything the Imperium has to offer, from Power-Weapons to Power Armour. Each more than a match for a Jedi. In addition to the Inquisition each Space Marine chapter has its upper eschelons, centries old veterans with the creame of the equipment at their disposal and Librarians, with Librarians think a Space Marine... but theyre Psychic.
This is ignoring the sanctioned Psykers and Psykers in general. Psychic power in 40k can, on its own, destroy worlds, sanctioned Psykers aren't QUITE that powerful, having been limited so that they don't get "ideas", but again, one is probably a match for a more Force based Jedi.
Star Wars has the Jedi and the Sith, powerful, but matched by the Imperium.
World Destroying:
The Imperium has the Doctrine of Exterminatus, that is, destroying any planet that is too far gone for them to retake it, normally reserved for the worst Chaos or Tyranid incursions it tends to be part of a "Scorched Ground" tactic of denying the enemy your lost resources. The methods of Exterminatus vary, from Virus Bombs, that turn the entire biosphere into a virulent toxic mush, to Vortex Missiles that do something between the extremes of: Destabilizing the planet on a tectonic level turning them into uninhabitable balls of magma... to destroying them outright. The Imperium as a fairly large stockpile of these superweapons and uses them comparatively often.
Star Wars has the Death Star and the Vong creatures of deeply depressing.
and this is JUST the Imperium of Man, one of the factions of 40k and assuming that the Star Wars Galaxy united against it, bring in Chaos (primal refletions of sentient emotion that take the worst aspects of the Imperium and make them even more horrible) the Tyranids (Omnicidal and Omnivorous swarms that strip planets bare to feed its implied they ate at least one galaxy before coming to the 40k one), Orks (Lunatic 8ft alien monsters who can easily kill a human with their bare hands without trying... and if they expect a bit of technology to work... it will), the Tau (Space Communists with some of the settings most powerful guns), Necrons (Omnicidal Mechanoid serveants of the Star Vampires who never die, terminator style they are capable of re-assembly on and off the battlefield), Craftword Eldar (The Remains of an ancient race who once ruled the galaxy, their goal at the moment is to turn the collective soul-energy of their entire race into a God... to kill the God of Squick they created milennia ago), Dark Eldar (Evil pirate cousins of the Craftworld Eldar who have turned killing and torture into an art for, their jetbikers are so skilled they can cut peoples throats with their bikes.)
Of course what would actually happen is that most of the Star Wars Galaxy would immediatly ally with the Tau (or maybe Eldar... maybe) and the Imperium would end up fighting them along with everyone else in the crazy brawl it is at the moment.
[/nerd]