Let print lab resize, or resize on export?

I have lightroom 2.5, Photoshop cs3. I have not printed out of the house in a while. so I sent a bunch of pictures to Costco to print at 4x6. so I told lightroom to export and resize 4x6 and when I picked pictures at Costco they were not super sharp. On edges of stuff you could see pixilation. plus there was some cropping which I forgot about.

Here are my options:
1) export pictures with no changes(leave them at normal size) at let Costco resize them to 4x6. If I remember right, there is more cropping, because the 50d pictures are not exact dimensions of 4x6?

2) let ligthroom resize picture to 4x6 at full resolution (150 dpi) and send them to Costco to print that way

3) Export pictures at full resolution and no resize, then have them automatically run through an action I just made in Photoshop which resizes pictures to 4x6 and resizes the canvas (adds) 1/8 of an inch on all sides so when Costco crops it will crop off that part and not touch the actual picture.

Is it better to let lightroom resize, or Photoshop? what dimensions are native on a 50d in raw? 4x6 / 8x10 / 5x7

Thanks in advance!!!

I never leave to chance that someone is going to do the resizing the way I want it done before printing. I crop,resize and sharpen before I send to a lab. Whether this is done from Photoshop or Lightroom the process is relatively the same. I do all of mine from Photoshop.

If you are exporting your image at full size and expecting the lab to print a 5x7 or 8x10 you do realize that you are going to lose part of the image. The 4x6 is the same aspect ratio as your camera so those can be printed full frame.

I can't comment on Costco's process or results as I haven't used them in years. I quit using these types of photo finishers and went to a pro lab. It costs me maybe a nickel more for a 4x6 but well worth the expense.

First, like Sheldon mentioned, a 4x6 won't crop substantially, but probably a bit on the borders to ensure full bleed printing. You can do your own testing, but in most images it will likely not be enough to matter. A 5x7 or 8x10 is entirely different and you are best cropping to those dimensions in Lightroom or Photoshop.

As far as the bad results you got back, that's really hard to say. One thing that experienced people do is turn off the option to have the Costco software "process" photos (to try to "improve" them). That may work for the casual P&S shooter, but if you've taken the time to get it "right" you don't want them to screw it up.

As far as file quality goes, if you want to resize I'd do 300 ppi -- in other words, create a 1200x1800 pixel image for a 4x6 print -- its' a proven high quality resolution for printing, and sharpen for output. Lightroom does them both when exporting, or in Photoshop you can do it with more control and a variety of tools.

Whatever you do, make sure your pictures look right at the same viewing size you will print at.