I did find out that when I use @Html.RenderPartial, the form-action is correct. But since I want the partial to be dynamic, I'd like to use an action to determine which partial to load. Therefore I tried using @Html.RenderAction, but that results in an incorrect form-action.

This sounds similar to an issue I had when working on getting XForms to work in a block type. What I ended up doing was building the action URL based on the current page's URL, so it looks something like this:

var urlResolver = ServiceLocator.Current.GetInstance<UrlResolver>();
var pageUrl = urlResolver.GetVirtualPath(currentPage.ContentLink);
var actionUrl = string.Format("{0}MYACTION/", pageUrl);

Then in the view:

@using (Html.BeginForm(new { Action = Model.ActionUrl }))
{
    // Your form...
}

That should get it to post to the current page the form is on.

I find myself in exactly the same situation as Maikel. Any other solution to this in EPiServer 7.5 perhaps? Or do I need to craft my own url via UrlResolver as shown by Chris above?

Has anyone been able to resolve this issue?  We have determined that XForms are not the solution we need because of their lack of layout customization and issues we would have with bootstrap.  I am trying to create the block that contains a form I am sent to a url with the controller and action method resulting in a 404 page. 

Take a look at Ove Anderson's version of this: http://www.eyecatch.no/blog/2013/01/using-xforms-and-mvc-in-an-episerver-7-block/

Then for customization, Ove also wrote this: http://www.eyecatch.no/blog/2013/09/full-customization-of-xforms-with-episerver-7-and-mvc/

With the help of those two posts, you should be able to create a XForm block with a customized layout. I've actually relied on those posts in a recent project, and my XForm implementation has been pretty successful.

Thanks for the suggestion Chris.  So do you not recommend developing forms in the tradional mvc style when using blocks or have you also had success with that in the past too? 

I only ask because we are going to have multiple forms on our site (different pages) but some of the data is being sent to third parties.  I honestly prefer to have the styling and development options of non XForm forms but at the same time I am running into routing roadblocks.  When I was in the episerver development training XForms were not really recommended.

Thanks for the suggestion Chris.  So do you not recommend developing forms in the tradional mvc style when using blocks or have you also had success with that in the past too? 

I only ask because we are going to have multiple forms on our site (different pages) but some of the data is being sent to third parties.  I honestly prefer to have the styling and development options of non XForm forms but at the same time I am running into routing roadblocks.  When I was in the episerver development training XForms were not really recommended.

I think it all depends on what you are doing with the form and its data. XForms are nice because they allow editors to create new forms and view its submitted data without outside developer interaction or codebase changes (providing that they are properly developed out). Out-of-the-box, they can cover for a large amount of use cases.

Though, as you've seen, XForm do have a less flexibilty, such as proper support for client-side validation and dynamic form values. There are ways around that, and given the time you have to implement XForms in your solution, you can develop the solution to use XForms that are just as powerful as standard MVC forms.

So I'm not for or against one method or the other; I've implemented both and continue to use both. You really just need to look at what you are building and providing to the editor, and make your decision from there.

And so you know, EPiServer is aware of the limitations and issues with XForms, and it is a topic of conversation when it comes to future releases of the platform.