It'll be difficult to get Guiliani through the senate. Sessions got through with 52 votes (+1 Sessions himself) because despite being controversial, he had good relationships on the senate floor with most senators. Some Democrats were outspoken in opposing him, but most weren't because in their senate careers they had compromised with Sessions before and had a relationship with him.
Guiliani doesn't have that relationship with anybody in the senate. There's a block of ~10 Republicans who dislike him and would likely split on him (5 giving in and going along with the president knowing that the 5 others will stick to their scruples), and for Guiliani to be confirmed, they'd need a solid 100% of Republicans to confirm him, because every Democrat will vote against, and many more Democrats will vocally oppose his position.
If Guiliani could be confirmed (I don't think he could be), then it's a toss up for "who's worse." In terms of the Russia investigation, Sessions is uninvolved because he recused himself, and it would seem like Sessions would not be willing to disrupt the investigation anymore or comply with his undersecretaries on this. Sessions is not a political idiot, knows the fallout from this, and also knows that his political and legal career would be over if he made the wrong move here. Guiliani would likely do whatever Trump wants and does not care. Outside of the Russia investigation, it's a bit of a wash... Guiliani is more centrist on issues that Sessions is far right on, like Guiliani has historically been pro-choice and has has supported public funding for planned parenthood. He also is not as extreme as Sessions on drug enforcement, though he still has an extreme position on it. GUiliani and Sessions differ most on immigration, as Guiliani has long been seen as one of the few Republicans to support paths to citizenship, immigrant rights, and extending services to immigrants/children of immigrants, but this has likely changed in the last 10 years... Especially as Guiliani has come to feed into the tea party, alt-right, and Trumpist/Populist wings of the Republican party, which are staunchly anti-immigrant. Sessions, of course, is one of the chief opponents of immigration reform and was one of the most ardent anti-immigrant legislators. That has continued into his AG post.