I hate rating stuff with numbers so i'll just make a list where the best shows are put first going along with what i enjoyed less being last (except for the special mentions section), of course with some comments, since doing this will already take bit i'll be going all out including shows you've seen:
First of i'll start bt explaining what UC stands for, that being Universal Century, its the universe where the main gundam series (the first gundam show) takes place.
After war Gundam X: Its clearly a spin off from the UC story (though stand alone so in other words its not connected to UC) and one of the rare gundams where the protagonist is actually an ordinary man with no real special abilities, its not the most complex show but it has a nicely done succession of events, an interesting world, a nice cast of characters, cool gundam designs and action.
http://www.youtube.com/watch?v=dJ8XH5JGyzQ
Next come two of the jewels of the UC timeline:
Gundam The 08th MS Team: another one of the rare shows where the protagonist is but just a simple human, still a very good show, also takes the most realistic mech approach compared to all other shows except IGLOO, show was made very good, excellent characters, good action and although simple good story:
http://www.youtube.com/watch?v=h_PKgztP0zw
Gundam MS IGLOO: it contains three series of OVA's each series consisting 3 episodes, the story starts before even the first Gundam and continues through the timeline of the First Gundam, this simply put is a masterpiece, it contains side stories so seeing the First Gundam isn't necessary, i really have to say this is not a gundam show that should be missed its great, it takes the most realistic approach compared to all the shows.
http://www.youtube.com/watch?v=UAXkPdgK7dQ
Mobile Suit Gundam Wing: comes with some of the best mechs gundam has to offer, it has good action overall, but characters are pretty blunt for most of the show,Heero though is kind of cool, the star of the series is though the Endless Waltz movie it was awesome, also if your going to watch Endless Waltz make sure you watch the movie not the ova:
http://www.youtube.com/watch?v=gsoqf_5k4TQ
Those where the stars of Gundam but their are some other good shows:
Mobile Suit Gundam 0083: Stardust Memory -takes place after the first gundam and is a prequel to Gundam Z, some didn't quite like it i for one did, was a good intercourse, also another show where the main character doesn't posses any special traits.
http://www.youtube.com/watch?v=yTEaue56tGk
Gundam 00: probably best looking show out of all of them (well it being one of the newest also helps :P), good artwork, good action but can't really say it was one of the best, as a gundam it was somewhat mediocre to good imho.
http://www.youtube.com/watch?v=kohWSTn0qZM
Mobile Suit Gundam ZZ: sequel to Zeta, third main installment in the series, its an okay watch and helps if you want to see more of the struggle in that universe, i liked the double Zeta Gundam.
http://www.youtube.com/watch?v=9mRT7EJ_24Y
Mobile Suit Gundam - Char`s Counter Attack - sequel to Gundam ZZ was a good movie, i liked the action mostly though and the Nu Gundam which is one of my favorites.
http://www.youtube.com/watch?v=gOARrcTbX1Y
Mobile Suit Gundam F91: In the UC timeline its a sequel to Unicorn (which is a sequel to Char's Counter Attack), it was a nice watch for me.
http://www.youtube.com/watch?v=3ZEcidqbmNw
Gundam 0080: War in the Pocket -personally i liked this one and no the little kid you see their isn't going to pilot a mech.
http://www.youtube.com/watch?v=i9Tt9MpfoF8
What i didn't liked so much descending order:
0079 MS Gundam (also known as the First Gundam): well i watched all of it just cause of the ambition of seeing all of the gundam shows but just couldn't get into it, this is where the second most powerful pilot in the gundam universe is, overall the story is actually quite good, but i recon there is just to much of a generation gap...
http://www.youtube.com/watch?v=Pp0zKv2UOUM
Zeta Gundam: had one of the most irritating cast ever (not to mention the most annoying and irritating main character Kamille), it was the first series where i ever wanted to see all the good guys dead, funny thing is Kamille is the strongest pilot out of all of them:
http://www.youtube.com/watch?v=cKm1iAnoSDY
^Nu este op-ul original.
Victory Gundam: my most painful Gundam watch damn i really hated this one.
http://www.youtube.com/watch?v=is7A_htB54g Special Mentions:
Mobile Suit Gundam SEED & SEED Destiny: my favorite gundam show but still this show, well is not for everyone, although it has pretty cool looking and equiped mechs the show puts the most focus on the characters and most of all their
emotions and how war eats and affects them on a more psychological level. Since the show puts a big focus on emotions is why this show is not for everyone since their can be a lot of emotional and scenes involving crying, pretty much i seen this as the only gundam show which has ever achieved of being antiwar, by bringing to attention many of the warring factors that has plagued us. The character art style also may take a while to get used to, but after a few eps it should sink in.
http://www.youtube.com/watch?v=4POpE501s4M
Turn A Gundam: not that good even annoying for some at first, but gets really interesting near the end imho, has the most powerful gundam of all times and is the conclusion to all the gundam shows.
http://www.youtube.com/watch?v=LU2PP8V-ZmA
Mobile Fighter G-Gundam: Unlike any other Gundam show this is a super robot anime (the only super robot gundam show), quite chessy and can have a few cooky looking gundams but it was one of my most favorite gundam watches, i loved this one.
http://www.youtube.com/watch?v=3pZ-I7iw16Q
Gundam Unicorn: haven't watched it cause its ongoing can't express myself regarding it.
Gundam Age: haven't watched it cause its ongoing can't express myself regarding it.
Notes: this is to give you the names and correct timeline for UC related gundams:
Mobile Suit Gundam 0079 (also known as First Gundam), Mobile Suit Gundam MS IGLOO: The Hidden One-Year War (this actually starts before the first Gundam but it might contain spoilers for the main show so if you plan to see them all its better to keep it after First Gundam), Mobile Suit Gundam MS IGLOO: Apocalypse 0079, Mobile Suit Gundam - MS IGLOO 2: The Gravity Front (the best one of the Igloo), Mobile Suit Gundam: The 08th MS Team, Mobile Suit Gundam 0080: War in the Pocket, Gundam 0083: Stardust Memories, Mobile Suit Zeta Gundam, Mobile Suit Gundam ZZ, Mobile Suit Gundam: Char`s Counterattack, gundam unicorn (this is ongoing), Mobile Suit Gundam F91, Mobile Suit Victory Gundam.
Gundam's not related between them or the UC timeline:
Gundam Seed & Seed Destiny, Gundam Wing and Endless Waltz, After War Gundam X, G Gundam, Gundam Age, Gundam 00.
As i said Turn A Gundam is the conclusion for all gundam shows.
There is also Gundam Evolved a short collection of CG clips that either remakes some of the moments in gundam, or shows some action scenes with gundams in 3d.
Well i think i pretty much covered it all.