Macross is after the original Robotech series. Robotech I liked, but Macross went in different directions. There are a LOT of them, so I'd say rent some and see if you like it before starting to collect. I have a thread for you too....PM coming.
That's incorrect. Macross is the first series which comprised of Misa Hayase (Lisa Hayes) and Hikaru Ichijyo (Rick Hunter). Robotech is actually three different animes put together (SDF Macross, Southern Cross, and Genesis Climber Mospeada).
Now in order for the three animes to fit together things were changed from the JP and US versions. When you hear the term SDF Macross they are actually referring to the original Macross which is the first part of Robotech. If you want the best Macross experience I suggest you buy the original JP version of SDF Macross as it has the real story without the changes made by Harmony Gold. I found Southern Cross to be kind of weak but Mospeada is actually pretty good.
If you really want to get into the Macross universe I suggest you purchase the original JP box sets of the three animes and continue from there. Out of all the different anime in the Macross universe, SDF Macross is the basis for all of them.
Now you don't have to buy them in a specific order to understand everything since they are all different stories which have nothing to do with each other. I suggest you start out with SDF Macross, then if you like it watch Macross Plus (one of the best OVA's ever made IMO). Macross Seven was pretty garbage so I would just skip that all together. Macross Zero is actually a prequel to SDF Macross whose main character is actually a secondary character of SDF Macross (Roy Focker).
To this day SDF Macross is still considered one of the best written and executed anime of all time and a lot of anime has tried to mimic it. The relationship between Misa Hayase and Hikaru Ichijyo is still one of my favorites in any anime.
Here are some amazon links to the versions you should buy:
http://www.amazon.com/Macross-Complete-Collection/dp/B001CK7OIS/ref=pd_bbs_1?ie=UTF8&s=dvd&qid=1219940923&sr=8-1
This is a re-release of the original Macross box set which cost $300 when it was originally released (I own it).
http://www.amazon.com/Macross-Plus-Collection-Two-Disc-Set/dp/B0009IOQXK/ref=pd_bbs_sr_3?ie=UTF8&s=dvd&qid=1219940923&sr=8-3
This is a 2+ hour version of the original OVA which comprised of 3 episodes. This is a better made cut than the OVA as the ending was redone and has some new scenes which put the story together a bit better. I suggest you watch this first then if you like it (I am sure you will) pick up the original OVA.
If you need more recommendations on Mecha anime let me know as it is one of my favorite genres so I have seen a lot.