I wasn't serious about that best ever. But, for me he's the best striker in the world. There are only 4 strikers who are for my as good as him, but i like Benzema's style more. My favourite striker alongside Benzema is Costa. The other 3 are Lewandowski, Suarez and Higuain, ofcourse i cannot put it in the way like "Benzema is better than Suarez and Lewandowski" but i have that, i think alredy well known love for players who are specialist in the dialog with midfield, link up play and key passes in the final third. Benzema is the best in that by far, so from my perspective, my taste, that kind of striker would be ideal for my ideal team. Costa as an all round teamworking beast, both offensively and defensively is also my favourite, but the way Benzema drops deep, goes wide, being 100% tactically responsible, working for Ronaldo is brilliant and puts him on the top fkr me. Higuain, Lewandowski and Suarez are pretty much capable of anything uprfont, goalscoring monsters, also very good in other parts like link up play, but as i said for my taste Benzema is no1. This discussion can be much longer and more detailed ofcourse
Other strikers such as Cavani, Aubameyang, Aguero etc, are arguably the lower class considering they're either one dimensional or overrated so Benzema, in the proper discussion, in the worst case can be considered as number 3 or 4 in the world. Cheers Viyut.