Pre-series 70 Colt 1911s are commercially known at the Government Model. If you can find one used, in good condition, go for it.
In the 1970s, Colt introduced the 70 series, which featured the slotted barrel bushing. Many people have changed this item for a solid one.
Colt introduced the 80 series Gov't model around 1983. This pistol features the firing pin safety (absent on earlier models), and they returned to a solid barrel bushing, although I did have an early 80 series that came with the slotted barrel bushing (which I changed to a solid one).
The designation Mark IV appears on later Gov't model pistols, usually the series 80 ones. The Gold Cup name has been a target pistol version of the Gov't Model that Colt has made for many years. If you can find one used that has been well-cared for and given a new recoil spring, it is worth considering.
People who are into Colt 1911s usually say the 70s series is the best so expect to pay plenty for a well-maintained pistol of this vintage. The series 80 are fine, but quality control by Colt has been up and down on these models for years. Any used 1911 should be inspected by a good smith before going to the range.
Finally, in the early 90s, Colt made "enhanced" versions of the Gov't model that feature a flat top slide, raked slide serrations, and a few other comestic touches. The traditonal round top slide model became the Colt 1991-A1, which has a parkerized finish and a flat plastic mainspring housing.
Now, Colt is now marketing something called the XS series which is a stainless steel 1911 with "custom" touches. The ones I have handled are nice but pricey.
Look for a good used Colt Gov't model and buy a book on what you can do with this pistol in terms of comestic or functional improvements.