Get a Glock 35 or 34.
I assume you mean USPSA because that's what we play in the USA. IPSC is what is played internationally. I often refer to USPSA as IPSC because it's easier to say, but the rules are a little different.
The Glock is the 2nd most popular gun to the double stack 1911's (aka 2011's). It has high capacity, low bore axis, and a short trigger reset. It's a high capacity gun made to shoot fast.
The glock 34, and 35 have a longer sight radius so you can shoot accurately more easily, but it also has a lightened slide so it cycles faster. The guns pretty much come competition ready, and the only thing you really need to do is polish the connector and you have a light 3 lbs trigger. You can further re-spring the gun to get a even better trigger. Almost all the modifications on the glock are do it yoursel drop in parts, and there are a lot of race parts for glock guns such as mag wells and tungsen guide rods, etc. Really all you need to do is resping the gun, maybe some good aftermarket sights, and high caps with extension if your shooting limited division. The glock 22, and 17 can be used too, but you'll need to make some mods like extended mag release, and 3.5# connector that the 34, 35 come standard with.
The Spingfeild xd 9 is interesting because you can use xd 40 mags loaded with 9mm. Thus you have cheap and legal high caps. Unfortunately it only holds 15+1 and you can put on extended basepads because your modifying a post ban mag. For USPSA/IPSC you really need high caps of 16+1 or greater. The reason is because it's usually arrays of 4 targets, thus if you had a 16+1 gun you can engage 2 arrays of targets (8 targets, 2 shots each) and still have a round in the pipe so your gun doesn't go into slide lock. With a 15+1 gun you either go into slide lock, or you do a standing reload. Ideally you want to do a reload while moving towards the next array of targets. To sum it up anything less than 16+1 is not much of a advantage than 10 round mags. The glock high cap with extension is 23+1 in 9mm, and 20+1 in .40, thus you have room to pick up shots you missed, or whatever.
The Berettas are OK, and some of the cops at our range shoot them. You can get 17 round mags in 9mm, but the .40 you will need a 15 round plus extension. The only extensions I know are some cheap quality +2's. There really are not a lot of race parts for the berettas. The cops that shoot them complain that the pins on the gun break or come loose every 5000 or so rounds.
I do't know of anyone that shoots the rugers, but they are cheap and high caps can be had. thus there is no reason you could't run on in USPSA, but there are better guns out there.
I would get a glock, in 9mm or .40. There is the power factor thing, but at this point don't worry about that. If you buy factory ammo then get a 9mm. It's so cheap to shoot. If you reload, or plan to be serious get a .40. The .40 makes major power factor, or can be downloaded to make minor and be even softer shooting than 9mm factory.
You'll also need a holster, belt, mag carriers, and 4-6 10round mags, or 2-3 high caps and 1 10 round mag. for holsters a $20 Uncle Mikes or Galico with adj tension screw will work. Don't get a fobus holster. It grips the gun too tight and will hurt your draw. Use a stiff dress belt until you get arround to getting a CR Speed High Torque belt.