Four certificates open the same door. As a teacher I am asked every month which one to take, and the honest answer is that it depends on your calendar, your nerves and your nearest exam centre far more than on difficulty. All four are accepted for citizenship. All four test the same B1 level. Let me give you the comparison I give my students, and then a piece of advice that matters more than the choice itself.
The four bodies
CILS, from the Università per Stranieri di Siena, is the most widely known and offers a version designed specifically for citizenship, the B1 Cittadinanza, shorter than the full B1. I describe it section by section in the CILS B1 Cittadinanza guide.
CELI, from the Università per Stranieri di Perugia, is equally respected; the level that corresponds to B1 is CELI 2. Candidates who prefer a very traditional exam structure often feel at home here.
PLIDA, from the Società Dante Alighieri, runs through the Dante Alighieri committees around the world, which sometimes makes it the most convenient option outside Italy: check whether a committee near you organises B1 sessions.
Cert.it, from Università Roma Tre, is the smallest of the four networks but exactly as valid. If a session happens to fit your city and your dates, there is no reason to avoid it.
How to actually choose
Ask three questions in this order. Which centre can I physically reach, and when is its next session with places available? Waiting three extra months for a famous name is a bad trade. Second, which format suits me? Download the sample papers from each official site and look at them side by side; the differences are real but modest, and you will feel within an hour which one reads best to you. Third, does the certificate need an official translation or apostille chain for my consulate? Procedures differ by country, so confirm with the consulate before booking. If you want the same comparison in a shorter reference form, we also keep a CILS versus CELI versus PLIDA overview on the languages hub.
The advice that matters more
Here is what twenty years of exams have taught the profession: candidates rarely fail because they chose the wrong certificate. They fail because they met the format for the first time on exam day. Whichever body you pick, the preparation is identical: reach a solid B1, then rehearse complete papers under time until the format is boring. The first part is the course; the second part is mock exams, and it is why the 
amo Italian app ships a B1 exam section with 35 complete simulations you can sit as many times as you need. Choose the certificate with your calendar. Pass it with rehearsal. The full roadmap is in the complete citizenship exam guide.
Note and attributions: CILS (Università per Stranieri di Siena), CELI (Università per Stranieri di Perugia), PLIDA (Società Dante Alighieri) and Cert.it (Università Roma Tre) are named for identification only; no affiliation or endorsement is implied. Formats, calendars and procedures change: always rely on the official sites of the certifying bodies and on your consulate for current rules. Not legal advice.
