Welp.. If you're limiting your choices to those two i'd go with the X3.. A lot of guys on here waited for its release to mod their boxes..
This is a quote from an installer from this site
http://www.copying-xbox-games.com/tu...ialid=00000027
I recommend 30 watts at the absolute maximum. Most people use low wattage irons in the 15 to 20 watt range. I have always used 30 watt irons, and while the iron may be just a bit too hot, it seems to work great for me. Also, you want to make sure that your soldering iron has a fine tip point. I think the finer the tip the better. My low watt, fine-tip, soldering iron was about $10. As for solder, I use .022 diameter radio shack solder. It is silver bearing solder, with a Rosin core (62/36/2). You can buy a 1.5 oz spool for about $2 at Radio shack
Hope that helps.. Doesn't really specify the tip but I think if it looks too big it probably is.. Keep in mind that you're working with small solder points.