Even if we consider Liverpool as a rich team but they are not going to have Xabi Alonso easily. In fact, Xabi Alonso is not a cheap option for any team and even if we consider Real Madrid as a team that wants to hire Xabi Alonso we can understand that are some teams like Liverpool and Real Madrid, and even Bayern Munich they are all linked to thing Spanis coach which can make the transfer much harder because regardless of dealing with Leverkusen to make them accept this deal, they have to race with beasts like Real Madrid for Xabi Alonso.
However, can't be sure if Xabi Alonso can still have a good performance in Liverpool or not if he leaves Leverkusen.
The way I see it, the safest option for Xabi Alonso is going to Bayern Munich. At Bayern Munich, he is guaranteed to have good players and play the kind of football that the club likes. The only challenge he'll face there is winning the Champions League league and as long as he does well in the competition he's good even if he doesn't win it.
Liverpool would be a gamble. Things could turn out fine or they could not. The expectation of filling Klopp's shoes is his biggest challenge. Klopp did so much for Liverpool, that pressure can be a problem for the next manager. Other than that, I feel Liverpool will be a good choice for him. They have a squad that he can work with and he can recruit some players from Leverkusen. Players like Floran. Liverpool has a less hostile environment to their coaches and is more patient with them.
Real Madrid to me will be a mistake. At Real Madrid, if you don't win the Champions League after 2 seasons the people are calling for your head. There is too much pressure on Real Madrid. Win a treble this year, if you don't win the league the next season, a faction of the fans are already against you.
Alonso's release clause is 30 million euros, that's big money but all of the three clubs can afford it so it might boil down to which team he prefers. The team that he likes the project the most.
It is also important to note that coaches that have been bought in this manner never do well in the clubs they go to.