Something you need to consider is the effect of coming out on your parents/family. Are you comfortable with shaking their beliefs to the point of unhappiness for them (not their disappointment in you, but rather their unsettledness with what they believe)? Do they force their religiosity on you? Can you live with it (I do, and have for decades, but I just address immoral things when I hear them). Just things to consider.

Having said all of that, some arguments against any religion are:

1. How do they know what they believe is true, especially given all of the thousands of other religions?
2. If there is one true religion, why has it not been revealed to everyone so that everyone has the same opportunity for fulfillment? Is it fair and just that not everyone has the same opportunity?
3. Why is it that, if there is just one true religion, that everyone seems to adopt the religion they are born into as the one true religion?
4. Since you know that morality is really the reduction of human emotional and physical suffering, are there any Sikh texts which do not do this? If so, you can point to the fact that a secular morality (reduction of suffering) reduces harm more than Sikh religious rules. 5.Have you read about the origins of the Sikh religion - can it be traced to something else? Has it borrowed from other religions? This would show it is not unique.
5. Are any modern miracles, such as medical recoveries, claimed by the Sikh religion? If so, you can ask why no one has ever regrown a lost finger, toe, hand, eye, etc.

Basically, a lot of the arguments that are in place against Christianity may be tweaked to disprove Sikh beliefs. No need to rush. Plan it out.