Most basic starters kits are good and will give you exactly what you need. You can easily grow from there should you desire but a person can brew beer great his whole life with beginners equipment.
The kit with 2 buckets is probably for single stage brewing and if you want to do single stage that is all you need. The 6 gallon plastic Ail Pails are perfect, no need for a carboy. If you want to go double stage, i.e. secondary fermenting, then I would suggest getting a 5 gallon glass carboy for that purpose. Also, if you go double stage you really only need one plastic bucket and one carboy.
Here is a general list of what you need to start. This is for double stage. For single stage dont get the carboy and add one plastic bucket.
1. 6 gallon plastic fermenter with lid (primary fermenter) The lid should be drilled to accept a plastic air lock.
2. 5 gallon glass carboy (secondary fermenter)
3. Long handle stainless steel spoon
4. Long handle plastic spoon (optional)
5. Hydrometer
6. Hydrometer test stand
7. Floating thermometer
8. Bottle caps
9. Bottle capper
10. Iodophor sanitizer or other type of sanitizer
11. Racking cane
12. 6 feet of 5/16 plastic siphon hose
13. Siphon hose clamp
14. Bottle filler
15. Bottle brush
16. Carboy brush
17. Carboy handle
18. Drilled rubber carboy stopper
19. 2 plastic airlocks
20. Bucket clamp for siphon tube
I cant really suggest the best beginners extract kit. There are lots of kits out there for beginners. Go to you local brew store or wherever you buy your equipment and tell them what kind of beer you want to make and they can help you decide what is best to start off with.
Truthfully, an extract with specialty grain or even partial mash is not all that hard. I would suggest that you at least get some specialty steeping grains to go with your extract. I think it will help the flavor a lot.
As far as the transition to all-grain, I dont know, I havent done it. Not because it seems hard but only because I would need more equipment, more time, more space, and more money to buy the equipment. Right now I dont have any of those and frankly, I am perfectly happy with partial mash brewing. I absolutely love the beer I have made and see no reason to move to all-grain. The point is that moving to all-grain is not inevitable. You can brew excellent beer with extract and partial mash.
Dennis