This topic is so, like, whatever.
There's just no pleasing some people. As ATCOs we're there to provide FIS, RIS, RAS, RCS (depending on where we work). The "S" in each case stands for SERVICE. Yep, we're down on the ground to make your life easier, not the other way round.
If we provide you with a choice, it is because we want to provide with the best possible SERVICE. If you are lucky enough to get a choice, then be good enough to answer with your preference - the very fact that we can let you choose means that we can accommodate any of the possible choices. As av8boy says, if we on the ground want to have you at a particular level, going in a particular direction and so forth, you won't get a choice.
Of course, after a choice has been made, the situation might change - in which case both ATCO and pilot can make requests of each other as required. At this point it is useful to know what you can and can't do, so answers like "I am VFR but can accept IFR" are indeed very helpful. But "Whatever" or "I don't mind" are not answers we like to hear at any time. Such responses suggest that you're not really bothered about receiving a service at all - at least that's the impression that we might get on the ground.
So, in short: Make the most of any options that we offer you with a positive response, because on another day you won't be given options at all.
LTP
(who believes "whatever" shouldn't even be in the dictionary, let alone CAP413)