No AR for any of the utility infusions.
What I'd recommend is to get a utility amulet, regardless of what stats you are wanting. If you're wanting to do fractals and don't have much AR yet, put a Versatile Simple Infusion in there - you can buy this from the golem at the start for 75 relics. Once you get to the point where you have "enough" AR for the levels you desire (or are able) to play, replace with gilded/mf/karma infusion.
After a certain point, more AR will not reduce agony. IE: 30 AR will not give any more agony resist at levels 10-19 than 10 AR; you'll take 1% damage per tick regardless.
For reference, here's the "max" AR needed at each level.
0-9: none needed
10-19: 10 AR will max you out. Level 19 has the same agony damage as level 10, so don't be afraid to play above 10 without any AR.
20-29: 25 AR
30-39: 40 AR
...keeps going up by 15
edit to add:
here's the chart showing you how much damage you take by FotM/AR.
Being 10 below the max isn't too bad, either, so don't be afraid to try FotM if you're lacking! All you need is an experienced group who knows what they're doing. Most agony ticks 6 times, taking 72% of your health over a period of 5 seconds, giving you plenty of time to heal/get to a safe spot/etc. Many dungeon bosses can hit you for that much instantly. I've run in the 20s with people who had 0 AR and we got through just fine.
And don't worry if you don't know what you're doing in Fractals or any dungeon. I (and many others) would MUCH rather teach you and then have more dungeon buddies than not have you play at all!
