Ditto--apples and oranges. What are you interested in doing? Just "la dolce vita" would be Portofino, not that you could not do that in Genoa, but the size difference and what's on offer is vast.

I think you could also easily do both with five full days for CT, unless you are an especially avid group of hikers.

Portofino is very small, and likely to be crowded in June, if that matters to you.

Not only is there a vast difference in ambience, there's a vast difference on size. Portofino has a resident population of around 400 people, Genoa of around 600,000.

What to do will vary too. There is a vast amount of interesting options in Genoa (e.g. 30+ museums) , see https://www.visitgenoa.it/en

While in Portofino there's only one public attraction, so you're likely to be concentrating on enjoying the ferry ride from Santa Margherita and maybe on to San Fruttuoso. For a full day's trip, maybe take a different ferry from San Fruttuoso to Camogli and return by train from Camogli train station.

Or Portovenere.

As others have mentioned, Portofino is very small. It relies on its past reputation as a little enclave for the wealthy yachting crowd. However, each time we have been we dislike it more and wouldn’t bother stopping by again as it is horribly overpriced (restaurants and shops) and it has little of the charm one may hope for. There are some truly world-class spectacular yachts there and the physical surroundings are great. Portofino park is wonderful for hiking and we love going to San Fruttuoso (water or hiking access only).

Genoa is a good sized city that has things to see, including the really good maritime museum and the usual cultural sites that a larger Italian city would have.

If I am choosing between the two, I would pick Genoa, and we don’t really like larger cities. YMMV

I agree on Portofino. They’ve even recently introduced a law allowing on the spot fines to be dished out to anyone blocking the pavement to take a photograph, which tells you a lot.

Genova is well worth visiting, as Europe’s largest medieval city centre. The covered market and streets around Pzza Colombo are worth exploring for food shopping and the excellent restaurants in that area, including some where you can eat out in the square, and the regenerated waterfront with its renowned aquarium up is also worth a good look round.

Tripadvisor staff removed this post because it did not meet Tripadvisor's forum guideline limiting each user to a single forums screen name.

#8 give it time…. You already can’t sit on the steps of the bridges, for the same reason

They are two completely different destinations, you can't say which one is better than the other.