How to best connect a temperature sensor to an aluminum block?
A lot will depend on the size of your aluminum block. The bare sensor takes more work to connect reliably, but for blocks less than (say) 2" x 2" x 2", it will give significantly faster response times than the encapsulated versions. For the prepackaged units, you're best off drilling a hole in the block and inserting the tube, or you can make a clamp for it. Be careful, whichever technique you use, to get good thermal contact - this generally means a lot of surface area in contact with the block.

If you go with the bare sensor, almost any expoxy will do. Just make sure you apply pressure to the sensor and squeeze out as much epoxy as possible. There's no need to worry about silver paste or anything like that, since there is almost no heat flow through the sensor. But make sure you also make a cable clamp to securely hold your wires to the block, so you don't accidentally rip them off. That means drilling (and tapping if necessary) holes to provide a strong attachment.