ME are not extactly optimized for mouse and keyboard. Unless you want better graphics and smoother gameplay, I would go with the PS3 version (The Lair of Shadow Broker is an "upright" DLC)
edit: Either way prepare for a huge dissapointment at the end of the 3rd ME. I invested like many others on the series when the first ME came out (I've played the PS3 DLC on an friend's PS3) and Bioware betrayed my love and dedication for the series storyline with the end of the trilogy (note that ME3 is great as a game aside from the end)
Oh also, you can use your PS3 controller on your PC if you want, download this http://www.motioninjoy.com/ and plug your controller in(also supports bluetooth if you have an adapter); it works like a charm.