I dislike Marker Drones as upgrades to most squads with the exception of Stealths and possibly firewarriors. On Crisis Suits they don't suit the unit's role. Let me explain it this way: The Tau Shooting Phase is a carefully timed thing. To get the most out of the phase, you need to give markerlight tokens to the units that need it and need the rest of the army to set up the killing blows created by those self-same markerlights while, at the same time, prioritizing your shooting order to account for the occasional choke.
Crisis Suits are units that will *very often* be the things that put the killing blow on numerous kinds of targets (transports, fliers, monstrous creatures, heavy infantry, etc.). This mean they will stand to benefit the most from markerlight hits, as their firepower is high quality and cover is most often the biggest impediment to their effectiveness. To give them marker drones, though, means they will be firing markerlights at targets that they, presumably, will either be destroying or crippling while using other marker tokens. They are, in other words, frequently wasted markerlights. Crisis Suits aren't the things that set up other units, they are the units you set up.
As for markers on FW shas'ui/Fireblade and so on, they're marginally useful but cater to a static role for your infantry, which I never do with FWs. It also can put FWs in an awkward position vis-à-vis fire order, since quite often it's my intention to pop a transport first and then let the FWs have a crack at what's inside, but I usually want my targets marked *first* so I can better plan out the shooting phase. It can still work, but these are sub-optimal markerlight platforms in my eyes. Besides, you really don't need *that* many Markerlights, anyway--6-10 should do it in most instances. Every markerlight you squeeze in the list is usually one less gun you will be shooting to cause damage. There is a point where it becomes a poor investment.