After playing with the new support items for some time now I have to say I love the gold items. They're awesome. Every one of them.

I used all of them in different situations and I think I tried all 3 on a Sona (who I play almost every game).
So basically I like the Spellthief's Edge on a Sona and other aggressive supports. It's good that you get both passive gold and gold from harassing as well, but that also means that you HAVE TO harass to keep up with the other support early game. I also like that there's the corresponding Bandit mastery to keep up with the harassing.
Ancient Coin and Nomad's Medallion are lovely early game, because you have to do nothing else than sit on the lane and take care of your carry and you'll still get coins and most likely more than going against a support with Spellthief's Edge. Yet again I like the Scavenger mastery that works along with this very well. I think Ancient Coin is awesome for more passive (not the harassing) type of supports like Soraka and Janna who can shield and heal most of the laning phase and only occasionally harass and aim for kills.

I've checked out the comparison of both items ingame for multiple times and I have to say that even though the Spellthief's Edge/ Frostfang falls off early game compared to Ancient Coin/ Nomad's Medallion in the long run both are just as efficient. Frostfang gives coins passively even if you don't do anything, but half of it's gold income comes from harassing (which you'll be doing in teamfights anyway) whereas the headstart of Nomad's Medallion evens out when you're spending less time in the lane and roaming more from lane to another.
Basically both have their uses.

Than last but least the Relic Shield and Targon's Brace literally EVERYONE used and loved at least where I play. (Still Platinum V, playing with players ranging from Gold I to Plat II). My favourite was the oh-so-abusive 2x Relic Shield start (support and adc both buy) which benefitted both the ADC and the support - but mostly support since the ADC would then lack damage needed for kill lane - since the passives worked both ways and both got increased gold from the last hits used with the item. You could farm A LOT of gold with this item if the carry had it too.

BUT IT DOESN'T WORK ANYMORE, BOOHOO! (Let's admit, we all saw this coming. Targon's Brace was never intended for ranged squishy supports or ADCs.)
Very discreetly without further notice (or at least I didn't see any) Riot quickly changed the tooltip and the item so that the passive last hitting works only with MELEE champions a.k.a the ones it was meant to be used by.
I found out about this the nasty way. I bought the Relic Shield in Ranked with a Sona, tried last hitting a minion with 100hp and cried out loud "WHYYYY DOESN'T IT WOOORK, IT'S A BUUUG" and then read the new tooltip and facepalmed, went back to base and changed into Spellthief's Edge.
Actually I was waiting when this would happen which is precisely why I didn't include the Relic/Targon's Brace starter into my guides (even though I actually considered it). Still when it happened I'm sad and happy at the same time. No more last hits for me and no more extra gold for my carry UNLESS I play Taric which I think I'll be doing since my favourite duo queue partner yehosera bought the pink skin for me :D We're gonna roll as the most rainbow bot lane ever with Taric+ Ezreal!
At least until the Snowdown skins come by and we'll go sing Deck the Halls with Silent Night Sona and Reindeer Kog Maw. Yes, I have probably the most childish dreams, but it's better than not having any at all. Games are meant to be fun so why not troll a bit (in the good, non harmful way). :)