Which is the most powerful summoning (effective and efficient)? I have been a great fan of Naruto for a long time, And I have seen lot of animals being summoned. But its been very hard for me to think which one of the summoning is the most powerful?

Please provide manga episode number or anime. I would like to check it again.
First thing first, I personally don't want to include summons from Summoning: Impure World Reincarnation Technique in my list because hundreds of dead peoples were summoned by this technique. One more thing, Tailed Beasts are not included in my list because Summoned beasts are generally animals bonded with a ninja. As ninjas can summon beasts they are sealed with, the beasts can also summon ninjas. If we look at tailed beasts, they are not animals, they are a pure form of chakra, they are immensely powerful and hard to summon and bond with. This makes them not in the Top 5 list.
Top 5 strongest summons in Naruto's universe
5 - Fukasaku / Shima aka Two Great Sage Toads


(source: nocookie.net)

Summoner: Jiraiya, Naruto Uzumaki
Manga Debut: Volume #41, Chapter #375
Anime Debut: Naruto Shippūden Episode #127
What makes it Top 5: Extremely proficient in the use of elemental techniques that require the nature manipulation of wind, fire, and water.

4 - Gamabunta / Aoda / Katsuyu



(source: nocookie.net)

Gamabunta
Summoner: Jiraiya, Minato Namikaze (Fourth Hokage), Naruto Uzumaki
Manga Debut: Volume #1, Chapter #1
Anime Debut: Naruto Episode #1
What makes it Top 4: He successfully hold the Nine-Tails down while Minato transported it outside of the village using his Flying Thunder God Technique.
Aoda
Summoner: [Sasuke Uchiha][17]
Manga Debut: Volume #66, Chapter #633
Anime Debut: Naruto Shippūden Episode #373
What makes it Top 4: As a snake, Aoda is extremely fast and nimble, successfully moving through an entire army of the Ten-Tails' clones while evading all of their attacks.
Katsuyu
Summoner: Tsunade (Fifth Hokage), Sakura Haruno
Manga Debut: Volume #19, Chapter #169
Anime Debut: Naruto Episode #95
What makes it Top 4: Katsuyu's clones can attach themselves to injured people, allowing its summoner to channel their chakra through it to heal the injured person.

3 - Nagato's Giant Multi-Headed Dog


Summoner: Nagato, Unnamed Fūma Clan Ninja (Male Animal Path), Ajisai (Female Animal Path)
Manga Debut: Volume #41, Chapter #375
Anime Debut: Naruto Shippūden Episode #131
What makes it Top 3: Physically strong and resilient, it gained additional heads every time it splits or been struck, and each duplicated head carried the black receiver and the Rinnegan like the original.

2 - Monkey King: Enma


Summoner: Hiruzen Sarutobi (Third Hokage)
Manga Debut: Volume #14, Chapter #120
Anime Debut: Naruto Episode #71
What makes it Top 2: He was easily able to incapacitate a reincarnated Hashirama and Tobirama Senju in brief hand-to-hand combat when they tried to keep him from transforming under the command of Orochimaru.

1 - Demonic Statue of the Outer Path


Summoner: Hagoromo Ōtsutsuki (Sage of the Six Paths), Madara Uchiha, Obito Uchiha
Manga Debut: Volume #29, Chapter #254
Anime Debut: Naruto Shippūden Episode #10
What makes it Top 1: Possesses great strength. The Demonic Statue can emit phantom dragons formed out of absorption chakra, which is capable of extracting the chakra of anyone they come in contact with. Most important, the Demonic Statue is also capable of emitting chakra chains from its mouth, which binds the power of tailed beasts, and can be used to both extract them from their jinchūriki and quickly seal them inside the statue.

*Most information was taken from Narutopedia.