Olof, S1mple, Cold, device, Guardian. The order can change depending on what metric to use, I guess.
Olof for 2 great majors, high peak and consistency (from '14 to '17, though kinda garbo these days).
S1mple for consistency (arguably top 5 for the past 3 years, HLTV just kinda shafted him in the '17 ratings) and the highest individual peak ever in CS:GO, which is especially amazing in a year with Astralis in it. Though he had less achievements, anybody who rates Olofmeister above him, but then Device below him, is a dumbass. S1mple had much better stats in 2018 than Olof had in 2015, and only lost to both Olof and Device in team achievements. If you value personal performance in a list of greatest players ever, then S1mple undoubtedly has to be somewhere at the top.
Coldzera for being the second person ever to get #1 two consecutive years, and doing so in an INFINITELY more competitive era than GTR. Also 2 majors (both of which he absolutely boss moded at), and one of the best, most consistent superstar playoffs players of all time.
Device has never shone as the ABSOLUTE best in a year, but anybody who thinks a guy who's been top 5 for the past 4 years (#3 in '15 and '16, #5 in '17 and #2 in '18) doesn't fit on a list of the top 5 CS:GO players of all time...is an absolute fucking idiot. Device is close to the easiest pick to be in the top 5, because unless you REALLY overvalue being #1, there's nobody except for Coldzera who could come even close to his scoring year-on-year. Also, let's be honest, he lost out on being the number one player of 2018 simply because S1mple had the best individual year anyone's ever had in CS:GO (and no, GTR doesn't count, considering the difference in level of competition). Oh, and device is ALSO a two-time major champion, and one-time major MVP (which is only trumped by Cold).
I kind of struggled with a fifth pick, because you can get into all kinds of arguments here, about consistency over peaks, and how much performance in years like 2013 and 2014 count ('cause I know a lot of people would whine about the exclusion of f0rest and GTR, mostly on the basis of nostalgia and personal bias of who they like, but I don't value those eras as being nearly as competitive as later times), but I just picked Guardian for fifth place because of his ultimate consistency. Device has, technically, had more "consistency" if higher placings give a player a bit more credibility in that sense (if you give points linearly from number one to number twenty), but you can't look past a guy who has been in the top 20 ever since the list was introduced in CS:GO, and his lowest placing is #17, with most of his placings being either REALLY close to top 10 (like his #11 placing in 2014), or within the top 10. He's had rough times in 2018, but over the history of CS:GO, you can't deny he's been a world-class consistent superstar, to the level that pretty much nobody has managed to maintain.
Olof Device Guardian Niko and maybe coldzera