In terms of trophies Liverpool's European victories dwarf Utd's.The best? Utd will always be the biggest until you surpass some of the records they’ve set like league wins, multiple European cups, 3 title wins in a row etc.
No doubt though we’d be a super club if Roman was here, on par or just below Real, Barca, Bayern etc.
But yes, with big finance we would have won multiple European cups, be ahead of league wins (we're ahead in Cup wins) and would have stronger support amongst the young fanbase than they do. We would have had 15 years of bossing them and the other English clubs.