Here's my situation:

Ticket 1: Air India (AI380): New Delhi to Singapore: Arrives in Singapore Terminal 2 at 7:20am
Ticket 2: Singapore Airlines (SQ16): Singapore to San Francisco: Departs from Singapore Terminal 3 at 9:25am

Total layover time is 2 hours. If Air India is delayed then I have even less time.

Option 1: I only take carry on luggage. Land in Singapore, take the sky train from T2 to T3 (takes about 5 min), go to the Transfer counter, get boarding pass, proceed to gate.

Option 2: Air India checks in my baggage all the way thru to San Francisco. I follow the same things as in Option 1,

Option 3: Air India only checks in my luggage to Singapore. I land in Singapore, clear immigration, claim baggage on T2, go to T3, go to airline counter to check in baggage and get boarding pass, go thru security, and then proceed to gate. This seems way too risky and almost a no-option.

What would you recommend?

I think Option 1 is your only option assuming the Air India flight isn't delayed.

I don't think Air India will check you through to SFO if its not on the same PNR. Neither airline will take any responsibility if you misconnect due to a late arrival..

Safest bet would be to take an earlier flight into SIN and enjoy the airport during your layover!

Good Luck!

I am not even sure whether Air India would allow you to board the flight (unless you have US passport) without a valid Singapore visa (if you hold Indian passport).

As long as you can show them a valid ticket out of singapore they should be fine with boarding you - as long as you only have carryon baggage

i would not do option 1 as well....like you said, it would be best to take an earlier flight....2 hours is a very short time for an international to international connection with separate pnrs....too many things can go wrong....