Hmmm, tough pick. I have a stealth class set up with the throwing knife, and it works really well for me. unless I miss, that is, (clank!) I prefer the frag over semtex just because I can bounce it around corners and get it into some tricky spots you just can't reach with a sticky, cooking is a necessity though since they roll around so much.
Third fave is the blast shield. There are few things more amusing than chasing someone around with your riot shield while they frantically try to drop claymores in your path or reload a noob-tube. And I can never seem to find any really good spots to camp, so I don't bother with tactical insert or claymores.