What is the best plugin for forms?
The best Marketo-integrated form is a Marketo form. (With which you can build various forms of multi-step progressions.)
In general the only "plugin" worth using is one that simplifies the use of the standard form embed code (i.e. allows the person building out a page to enter a numeric Marketo form ID instead of copying-and-pasting the entire embed code). A plugin that only allows browsing for form names that are then simplified to IDs in the embed code would also be alright. Anything that tries to go beyond that is introducing reliability and rookie DoS issues into your environment.
And which plugin can help us sync up all contacts in our marketo database?
I don't understand the question. Please be as explicit as possible about your business specs.
He wants a Marketo Form API insertion. There isn't a plugin for that.
As you mentioned, a Marketo Page+Form combo will be simpler to implement for this situation. Julien Picaud suggest you search here because that topic is well covered.
If you want to do multi step/page forms on another CMS, you can do that if you leverage the API.