Howdy Aedrick, and et al.,
Merry New Year! Welcome to the forum. Let me also have a go at this thread with some additional considerations for you to ponder. First, all of the three are well built pistols, otherwise sales of them would not be so intense. Each of those would generically suit the broad category of a “range” gun. So far the only constraint is your price range. Given the current market climate you might be real close to your limit on picking up a new gun in that range. Your mileage may vary depending on where you are and what retail outlets you have available to you. There will be those who advocate the internet purchase method, just be sure to proceed with care and identify all costs affiliated with that approach.
I would also join in the chorus to advocate that you make an effort to try each of them out before purchasing. Ask about, see if friends have one that you can try or find one of your local shooting clubs < IDPA, USPSA, etc >. Also there are the range rentals where you can have a go at several platforms to give them a test drive.
While they all shoot well < shooter capability + quality of ammo + gun's capability = resulting accuracy > there are differences, it all depends on what level of significance you put on things, they all drive differently.
The G17 & G34 do share the same frame so when you grip either one the grip dimensions will be the same. How they feel both statically and when shooting are very different. The G34 can come with different connectors ( you can specify that when you order ). The issue of sights is also a consideration too. I believe the G34 only comes with adjustable sights where there are several order options with the G17 ( plastic, steel, night sights ). This is not a big deal as it is really easy to change sights as an after purchase option.
The 34 also comes with an extended slide release while the 17 only has a slide stop. Again you can obtain the factory part and install, or there are several after market designs available too.
The XDs are available as just the pistol or as a kit where you get several magazines, holster, and magazine holder too. It depends on what you want. Note: I've never seen one of the kits with a left handed holster, so if you are left handed you need to be aware of this.
The issue of barrel length is another one of those preference things. Some folks really like having that longer sight radius to get the pistol aligned on target. The additional barrel length also translates “sometimes” into some added velocity which may or may not be important depending on the distances that you are shooting ( if shooting under 100 meters you are really going to find it tough to tell ).
A SIG 210 would be really fun for a range gun but yes, the price is substantial. Also so are the cost of the magazines too!
Accuracy of the SIG P226? I can only convey my personal experience. I have a factory refurbished SIG 226 which shoots well. I can consistently print better groups with my P226 over my G17 using ammo from the same box of Winchester White box. However, they are not that much better at 25 yrds. We are talking a fraction of an inch difference at those distances. Again, since you've not established your range criteria only you can assess what you are looking for and what is important.
Ok, some quick background, I use my pistols for fun and serious stuff so they are not just for “range” purposes. So given that I've got some very different needs to address with my pistol platforms your mileage may vary. While I considered purchasing an XD, there were engineering, maintenance, and durability considerations that were just not what I wanted ( this is important as I've got my own criteria ). Depending on the number or volume of rounds you intend to shoot through each pattern you may care to adjust your purchase consideration.
Additionally, I choose to do my own maintenance and gunsmithing so I wanted pistols that would accommodate that. At a minimum I run about 2k annually through shooting matches and a few rounds more for just practicing. Each pistol platform gets a good share of that annual amount.
Just as shopping for all other things figure out just what you are looking to use it for and then look for features that will help you. Test driving is a good thing if you are not in a hurry. Realize that all pistols are machines and some folks take better care of them than others. Each design brings things to the party that could be fun. Again, each of them are well made pistols so even if you don't do a lot of analysis you are still going to be in good shape. I've not seen the generally approved recommendation of “ buy them all! “ issued so let me have a go at that! Good luck in your shopping and acquisition. We'll be looking forward to that range report soon!
Cheers!