I'm not sure there's such a thing as 'the best' as owner opinions are always going to be subjective.
My vote for the most realistic is the Baikal Makarov - not so much a replica as a CO2 variant of the 9x18mm firearm.
Others I would recommend are the Anics non blowback pistols as most sights are adjustable and power tends to be higher than other replicas. Then there's the Umarex P08, which works on the same principle as the Anics and performs very well. It's a great looker too if you like Lugers.
John M
Currently looking for Baikal Makarov pistols with the following prefixes to the serial number: 98, T01, T09, T21, T22
Prefer boxed or cased but will consider loose examples too.