This appears to be old but to correct the above answer, Bitcoin Gold used to use the Equihash algorithm but recently forked to the Equihash-BTG proof of work algorithm in order to keep in line with the protocol's main objective, ASIC resistance.

As for which protocol is better? I suppose for some that is a matter of opinion but if you ask me (and the majority of the ecosystem as evidenced by the price), LTC has it all over BTG in terms of developer interest, liquidity/volume, price, propagation, potential use cases, etc.

The GPU-mining ship sailed long ago for LTC.

To answer some questions to the best of my ability:

But wasn't this tried already with Litecoin via Scrypt mining algorithm?

Yes, this was tried with Litecoin.

is Bitcoin Gold now a better alternative?

This is a matter of opinion.

What's Bitcoin Gold algorithm?

They forked to the Equihash-BTG algorithm.

Can it become minable by ASICs at some point too?

Yes, every algorithm can be mined by ASICs, but some algorithms are more expensive to produce specialized hardware for, than others.

Could Litecoin switch to this algorithm to be ASIC resistant again?

Yes, Litecoin can switch algorithm if there is consensus to do so. Whether or whether not Litecoin would become ASIC resistant, is a matter of opinion, as ASIC resistance is a very debatable topic about whether it is possible or not.

I just started reading The Definitive Guide to Gold, a free 65-page ebook that talks about how gold is an important part of financial success. It’s pretty interesting to see how technology is changing the gold industry.