I've got a 12V Ryobi that I bought at HD for about $50, and got a free stud finder. Before that I had a 7.2 V Sears, which really handled most 1 1/4" to 2" screws without any difficulty. I just wanted a little bit more power, and an extra battery.
For woodworking, I don't see the benefit of an 18V drill/driver. I've driven 4" #10 and #12 wood screws into studs with the 12V (here's a hint - rub them with a little soap and they go in 10x easier), but I do that rather occasionally. I don't have to drive 200 deck screws on a daily basis, or install an entire set of kitchen cabinets. For project assembly, pilot holes, countersinking, the 12V tool has more than enough power. I also appreciate the weight of the tool - I don't want to be lifting extra weight that I don't need.
For woodworking, I don't see the benefit of an 18V drill/driver. I've driven 4" #10 and #12 wood screws into studs with the 12V (here's a hint - rub them with a little soap and they go in 10x easier), but I do that rather occasionally. I don't have to drive 200 deck screws on a daily basis, or install an entire set of kitchen cabinets. For project assembly, pilot holes, countersinking, the 12V tool has more than enough power. I also appreciate the weight of the tool - I don't want to be lifting extra weight that I don't need.

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