In terms of overall usefulness no summon beats the Animated Weapons imo. They are not only fairly tanky and can spread out but also they each have several uses of special attacks (Pike: Knockdown, Warbow: Wounding Shot and Great Sword: Flames of Devotion) which adds a lot of offensive potential (for example more accuracy than a standard attack).
The Dragon has one (or two) advantages: he is very tanky (huge health pool) and takes up a lot of ground space, blocking a big area. While his standard attack is weak, his active attack abilities (fire breath, tailswipe and so on) do scale very well with his high Power Level and thus have great effect. Only if you used them all up he starts to suck offensively.
The second advantage is that a Dragon can profit from an Ancient Druid's "Wild Growth" spell. This is just hilarious: not only does it give the beast summon the Robust inspiration for the entire summoning duration (Wild Growth has no duration, it's basically permanent for that summon), making it even harder to kill - it also makes it bigger. You can imagine how cool an already huge Dragon can be if you enlarge him even further. What a mountain of an ally. He will block an enormous amount of space for you. This can be a disadvantage, too: if the space is verys limited he might get stuck. But usually it's very useful because he will occupy a lot of enemies with his big size.
This also works with Drakes (all summoned beasts), but they are considerably weaker.
If you like Wildrhymer I'd say Animated Weapons is good enough though. Also Many Lives Pass By (phrase on PL7) is accessible as multiclass. The automatically summoned Skeletons don't count towards the summoning limit and "stack" with other summons (and Animal Companion). So you can have Chanter summon + Animal Companion + Skeletons.
A nice synergy of Chanter + Ranger is that you can revive the Animal Companion as often as you want with an invocation. So it's not the end of the world if the Animal Companion goes down early. It cannot get injured so it's as good as new after getting revived.
My preferred multiclass for summoning is Troubadour/Psion because it can add lots of "temporary allies" (aka charmed/dominated enemies) to the collection of summons. Also both resources (phrases and Psion's focus) work the same for a Chanter/Psion and you will almost never run out of casting fuel (unless you get hit all the time which usually doesn't happen due to so many alternative weak cannon fodder targets).