KMS or MAK for RDS 2008

Neither! RDS licenses aren't done via MAK/KMS product keys. It's done via your Microsoft agreement information. You activate your license under the RDS licensing manager. Currently only OS and Office 2010 installations can use MAK/KMS product keys.

-Matt-

My mistake it is for office 2010 on rds servers

Products are licensed per system. So pick either one. BTW, I forgot to mention you can mix activation methods too.

Products are licensed per system

that should be Products are activated on a per system basis.

Yes but should I do a mak on the rds server? Or is kms better

Which better is a matter of option or based on your company size. Both methods accomplish the same thing. As I mentioned before you can mix the two methods. MAK is recommended for companies with 50 or less systems. Plug in the product key and complete the activation via Microsoft's activation server on the internet (or phone). KMS is for those companies that don't want to have to use the internet for activations. KMS sites have to setup a KMS server, the equilivent of Microsoft's activation server, for inhouse use. This is typically for larger companys.  But you could could also choose to use KMS for even a small company. I read it somewhere that Microsoft was going to require KMS method for those with 200 or more systems. But I can't find it again.

This EE post mentions pro/cons of each method: https://www.experts-exchange.com/questions/24406442/KMS-vs-MAK-activation-for-Windows-Server-2008.html.
This article also mentions some good information: http://technet.microsoft.com/en-us/library/dd981009.aspx.

-Matt-

Well I have 100 users on rds.

Again it's not about users or RDS. It's about Microsoft OS and applications deployment. Each OS (Vista/Win7/Svr 2003/Svr 2008/svr 2008 R2) or application (Office 2010) that's deployed will have to be activated. I can't recommend which method is better for you as I don't have all the needed information. That's why I've provided various resources for you to reference so you have the information to decide what's best for your needs. The only hard information I can provide is Microsoft recommendation of using MAK for those comapnies that have 50 or less machines.

I would use KMS on the RDS server. You do have a limited amount of activated with each MAK key. You can have an unlimited number of activations to the KMS server. With the KMS server you also do not have to activate as the machines will contact the KMS server in the background using a DNS entry created while installing the KMS server. As stated by previous posters you can have a mixed environment. The default silent install I use is a KMS install. I then change the key to an MAK key if I know the PC will be offsite for an extended amount of time without VPN connection. You can always change an Office KMS install to MAK at a later date.