Just wonder. I don't complain, I have good sales there but the upload and keyword processing is a bit annoying 

I find Shutterstock overall to be the best financially, but you have to keep uploading new material to maintain a good cashflow. Istock is the most consistent with older portfolios.

Everyone has their favorite.  There is no "best" for the entire population.

Istock continues to be my best seller too.  I do find the uploading process tedious, and now especially the new model release requirements are adding significant time to my work flow there. 

But I continue to jump through the hoops because they are nearly 40% of my income. 

Istock is definitely my top earning agency, 2-3 times more than the second best one.

Not only that, because it is no longer owned by an induvidual, if you encounter any problems, I assume you can ask someone else in the higher level to review the matter. I like their Scout sytem. Other than that, I have never dealt with anyone else so I cannot say for sure, it is my hope though.

...20% for non exclusives and 40 % commissions for exclusives are too low.

I agree, they should increase it by at least 10% but after being taken over by Getty, who only pay 20% to non-exclusives, that isn't going to happen.  It has given some of their rivals an excuse to cut our commissions, so we end up losing even more.  They spend lots on advertising but it does hurt when they take 80% of my earnings.  Going exclusive for less than 50% doesn't appeal to me.

results really vary - over last 2 years my is portfolio went from 400 to 600 - sales were rarely better than 3rd or 4th [after dt, ss and usually BigStock], except fr 1 or 2 EL blips.  so i dont upl very often to is. 

once again, i'd strongly discourage newcomers from going exclusive - my sales lines weave in an ut for the top 8 that produce for me -- only dt and ss consistently come in 1st or 2nd.  the market is too volatile to risk it all w 1 agency for both near and far term.

My experience is pretty much the same as sgcallaway1994's.

IStock has an artsy image, a nice looking web site, and some social networking fluff. Take that away, and you have a microstock that pays you 25 cents just like the others,  but -
 - takes 2 weeks to review an image
 - rejects a lot of images that the others accept
 - doesn't support FTP
 - has a tedious, rigid keywording system that just doesn't work with some images

Can't agree with most of what you wrote, but as always, YMMV:

 - 25 cents
Maybe you're getting IS mixed up with other sites that pay you pennies for sub sales and let the buyer take the largest size available? My overall average RPD at IS is $1.06, ranging from $0.80 back in '07 (when prices were lower) to $1.17 last month.

 - 2 weeks to review an image
I've seen as short as 3 days and as long as about 12. The average is 6-7.

- Rejects a lot of images that others accept
My experience is exactly opposite. IS accepts far more of my images than do DT, FT, or even SS. At the current pace, my port at DT & FT will be 1/2 the size it is at IS before year's end. (It doesn't help that I've stopped uploading at DT and FT .... )

- doesn't support FTP
Who cares when you have Deep Meta? Even if they had FTP, I'd still use DM.

- Tedious keywording system that just doesn't work with some images
Well, if you don't use DM, I'm going to have to agree with you on this one. Even if you do, it is true that some images -- very, very few, but some -- don't fit well with the CV. But I still prefer having a CV to not having one. Other than the image itself, keywording and a good search system is the single most important factor in your image being found.  As databases become larger and larger, this is going to become an even more critical factor in buyers migrating to IS from their competitors. With the CV and proper keywording, it's possible to more quickly drill down to the images you are looking for. On most competitor's sites, it can be a nightmare. The CV is far from perfect, but it continues to get better every month.

I guess it goes without saying (though that won't stop me from saying it) that IS is my favorite site. They've accounted for 30% - 40% of my income since I joined them (well, a few months after), they have the only forums I find worth reading on any micro site, and their reviewers are the best (and most consistent) in the biz. That doesn't mean they accept every image I submit (my AR is still struggling to get over 80% there), but it does mean that when I get a rejection it's usually for a reason that I have to reluctantly (or sometimes enthusiastically, as in OOPS!) agree with. Rejections at DT, FT, and SS usually result more in "what was the reviewer smoking?" reactions.

But 20% commissions do suck.

But 20% commissions do suck.

And given IS is a good earner for us, you can imagine how much money they are doing - even if they spend more in advertisement (as it's always the explanation given for our low share).