"He will gladly compare them."

Translation: Er wird sie gerne vergleichen.

[HallieGray]

"Er wird gerne sie vergleichen" is unfortunately for me an incorrect assortment of those words.

[Lexht]

gerne should go close to the main verb. Pronouns should come immediately after the inflected verb.

[Soglio]

How do you decide between using "gern" and "gerne"?

[wataya]

You don't have to. You can use them interchangeably. 'gerne' is slightly more formal but nothing to bother about.

[Soglio]

Thank you. Whew! One thing I don't have to worry about. ;-)

[deactivated user]

The penny drops.

If you think of the sentence as He will + gladly compare them then it comes out as er wird + sie gerne vergleichen. .

Think of the verb as gladly compare and the auxiliary as he will, rather than he will gladly + compare.

[Peter_Duffy]

any reason why "Er wird sie glücklich vergleichen" should not work here?

[deactivated user]

Yes, glücklich is state of being, Du bist glücklich, etc.

When used as an adverb, happily, gladly, etc. You have to use gern, or gerne.

[Peter_Duffy]

thanks Peter