Printing an 18x24(ish) print.... when does MP start effecting results.

I have a few choices I am trying to pick from. and I am not sure if I could go with some of my older stuff (namely from my 20d) or if I should go with something that I've shot with my 50d. I have a buggy who made the (very valid) statement that they've printed bilboards with much less than 10mp (such as the 20d) but you don't get 'up close and personal" with those, like you do a print hanging on a wall....
I am just hoping for a little input before I make my decision tomorrow.
I have a few examples of some of my possibilities here:

[EDIT]
I've disabled right-click on my website, so I'm not sure how to show you the image here.... without a link... forgive me.
If mods or anyone has a suggestion, please let me know, and I'll take the appropriate action to 'fix-it'


[RE-EDIT]
I tried using a shortened URL and that didn't work... go to this gallery, cause I give up... #1 and #3 are the 10mp candidates, $19 and #20 are the 18mp candidates.....
http://jpbimages.com/p​323849192

I have 24 x 36 images that have been printed and framed coming off a 8mp and they look great. Like you already stated, photos that size are not meant to be up close and personal. Most folks will stand back some since they need to be able to see the whole photo at once even when they are hanging on a wall. I like 3 and 19.

I try to use 360 ppi as thats the best quality my Epson R2880 printer will deliver, that means you need 8640 x 6480 pixels. But I can go as low as 120 ppi before the quality drops through the floor, its noticably not as good, but bearable. At that setting you could get away with 2880 x 2160 pixels.

I tend to pixel peep prints so I'm maybe over critical, because as the last poster mentioned, most viewers will stand further back to see a larger image.

I have a 6MP image at 30" and a 10MP image at 55" that both look great.

Printing FAQ.

I'd say that as a rule of thumb - and a very loose rule of thumb at that because, as said above, so much depends on viewing distance and because what is considered acceptable/good/excell​ent quality is very subjective - that any uprezzing to as much as 2X will give very good results. For Epson that means starting with 180 ppi and for Canon, HP and most lab printers, 150 ppi. More uprezzing than 2X with very good results is possible, but it requires better software and better technique. For instance: http://www.outbackphot​o.com/workflow/wf_60/e​ssay.html Other good options are Lightroom, Perfect Resize, and Photo Zoom.

tzalman wrote in post #14994149
I'd say that as a rule of thumb - and a very loose rule of thumb at that because, as said above, so much depends on viewing distance and because what is considered acceptable/good/excell​ent quality is very subjective

^
Keep in mind that the relative quality of a 3504x2336 pixel image from a 20D printed at 8x12" (292 ppi) and viewed from 12" away is identical in perceived quality to the same image printed to 40x60" and viewed from 60" away. So you really do need to consider the viewing distance of the viewer from your print.

I have prints from cameras ranging from 4MP point and shoots up to my 12MP 5D Classic, all printed either at 12x16 or 12x18. Because all the images have what I consider decent "visual appeal", they all come across very nicely at a "normal" viewing distance (they are framed and hanging on my walls).

As to close-up viewing, well, sure, the 4MP, 5MP and 6MP do get soft in the details. They stay on my walls, I wouldn't submit them to some kind of contest.

But, I have prints from my 8MP 30D and I can get really close! I've actually looked with a magnifying glass at close details and have been impressed! Of course, the original image needs to be sharp for that kind of scrutiny, but at least that may give you a good idea of what you are working with and what to expect.