I recommend the RPM brand of logger. I use it myself and have found it to be very user friendly. The sensors and cables are very reasonably priced. Randy the owner / operator is easy to get a hold of and will help you through any of the questions you might have. Check them out. This is not a new fly by night operation. You will probably get a lot of people saying buy a RacePac and be done with it. I can't argue that they are top of the line, but look at there sensor prices first, and they don't do anything that the rpm won't do.
As to your second question, each offers different info that is useful. I would first opt for the o2. It will give you an overall shot of your fuel curve. I just got my o2 installed and if helped me immediately. With the o2 in the collector it won't tell you if one cylinder is lean so you have to decide if you want to put bungs in each tube and you can move the sensor around or just in the collector. Same for the EGT probe. The EGT can give conflicting data with alcohol if you are way lean, or way rich so keep an eye on plugs also.
With the basic package you can log rpm, drive shaft rpm, convertor efficiency, and voltage. Then add as many sensors as you want. I have added o2 and vacuum sensors to mine. Next will be oil pressure and temperature for trans and water. Just my 2 cents.
Curtis
www.rpmperf.com