For ME1, the PC version came out somewhat later than on the 360, and they took the time to improve in a few areas. The graphics are somewhat better, and the interface is vastly improved (other than that, I'm not sure).
The PC version is certainly "better", although personally, I find it more enjoyable to just sit back with a controller in my end in front of the TV, confident that the game will run as intended on the console, not needing to worry about interfering with anything else I might need to do on the computer (I find minimizing games often causes issues).
So, if you have no personal preference as to what system you play games on, the PC version is better, simply because it was released later and improved upon in the process.
Either way, I suggest you take ME2 into consideration when choosing. The connection between the games if you import a ME1 character is certainly worthwhile, and it would be best to have both on the same system to make use of that.