As far as the statement of:
Heard that Dell monitors are best in class
I wouldn't say they are the best out there. Some are Good, some are OK, and some are Junk.
As far as specific model to purchase it comes down to features and specs mainly, as well as appearance in some cases as well.
As far as Dell monitors, I dont buy them myself, but instead get them for free or very inexpensively when people get rid of their Dell computers.
Dell, just like HP, and other computer brand monitors are basically their brand name placed onto the guts of other display manufacturer displays in which Dell has a contract with a company that makes inexpensive displays to make them say 100,000 of a specific model with the Dell name on them. The reason for some being good, ok, and junk is because they sometimes cut corners in pricing to be competitive that leads to "you get what you paid for" of quality. So cutting corners to make low cost displays can sometimes lead to problem models or models that lack in performance.
For this reason, I like to not buy displays that are computer re-branded displays, but instead buy from a manufacturer of displays that are well known for quality who have a good warranty. I usually buy Samsung displays because I have had very good luck with them. They may cost more than the Dell or HP display etc, but at least I know that I have a quality product that should last me with no troubles.