If you contact Marriott Rewards and fax them your prior stays with Hilton, they should comp you to gold and give you a fast track to get platinum. This is usually accomplished if you stay 18 nights in 3 months.

I have not had much experience with Hilton, but I can vouch for Marriott's service being consistent on a high level. The biggest differences between gold and platinum is the platinum welcome gift and the platinum guarantee to book a room with 48 hours notice (with rare exceptions). Marriott backs their guarantee of room type, concierge lounge access/free continental breakfast on weekdays at FS properties (excluding resorts), and the platinum welcome gift with a promise to pay cash if not met. I have received $250 this year for not getting my platinum welcome gift.

If you maintain your prior stay history at Marriott, you will probably qualify for Platinum Premier, an unpublished level. The qualifying levels are not exactly clear, but most people who have this level have stayed at a Marriott property for 125 paid nights/year for at least 3 years in a row.

Marriott also calculates elite status with an rolling calendar year. Unlike Hilton, this is not a written rule. In addition, Marriott also has lifetime elite status. You can qualify for this if you have been a Marriott Rewards member for at least 12 years. A search will provide full details, but the basic requirements are:

lifetime silver (1.5 million points earned with 600 paid nights) This is not that valuable since holding a Marriott Visa card will give you the same benefit.
lifetime gold (2 million points earned with 800 paid nights)
lifetime platinum (3 million points earned with 1000 paid nights)

Although you are suppose to requalify each year to maintain elite status, there have been cases where people have gotten comped to an extra year of gold or platinum. I met one guy in a concierge lounge last week who got an extra year of platinum during a slow year of travel.

My experience at the NYC Marriott Marquis was the opposite of DADISGARYK. I found the service to be excellent, and I got a complimentary upgrade to a city view room. They have one of the finest domestic concierge lounges in terms of food served and the general amenities.