Obviously my attention to detail is lacking as I didnt note the last two questions...
iamjosh summed it up pretty well...what do you like the look of regarding live rock? I suggest looking at several types at LFS's and seeing what it is that you like or dont like then go get some! The different types vary from region to region. I didnt choose Fiji cuase it seems like everyone has that in their tanks and I wanted something a little different. I chose Kaelini as it had just hit the market, was nicely shaped, and had excellent coralline algae colors and was heavily coated on the rock. Recently I have seen some great shaped Tonga/Eva that appears as a fused conglomeration of Tonga Branches and just blew me away with the coralline algae coverage, color and tons of life that had survived shipment. In fact I would have bought a couple of hundred pounds if they had had that much in stock! I will do so the next time I am in San Francisco and they have some that nice again!!! But these two types of Live Rock are just my personal preference and in no way am I implying that its better than any other types out there. Again, check various types out and choose what fits your taste.
As far as base rock and live rock I am not exactly sure what you mean. Some live rock is sold as base rock and its usually mediocre shapped pieces best used as a foundation for your more choice live rock pieces to be stacked on. As such it is usually cheaper. However a very common practice is to use dry calcium based rock such as a rock refered to as "Lace Rock" to be used as base rock for your more nicer shaped pieces of live rock. This "Lace Rock" can be had in some very nice shapes, used as ledges and what not and will quickly be colonized buy bacteria and become live as will as become coralline algae covered. It is usually considerably cheaper than live rock and is often used by those on a really tight budget or those with HUGE tanks that require a lot of rock and its too prohibitively expensive to completely do in Live Rock.
I hope the above information adequately answered your concerns and questions.
I agree with Ritsuko Nashida...I have both Kaelini show rock and Tonga/Eva rock in my 180. I am very pleased with the my live rock both size and shapes. I suggest either hand pick your rock from your LFS or order a box from a reputible seller/sponser. I did a little of each. Just my 2 cents.
I originally started with a 45 lbs box of Kaelini. It came with all of about 5 peices 3 of which weighed more than 10 lbs each including one that was obviously a table top acropora at one time(barely fits through the opening on one end of a 75 gallon AGA aquarium its so big). The other two were about soft ball sized. I got is shipped Fedex over night from www.anchofish.com which I believe is now defunct for under 200.00. The rest of my rock except about 30 lbs is all DIY rock seeded with Kaelini or Tonga/Eva. DIY rock is kind of a neat option too! You can make the rock shaped and sized to fit your needs and have a potentially awesome looking reef in a few months. In fact all of my frags are sold mounted to small pieces of DIY rock rubble that I made using styro-foam egg cartons for molds. My sump has 45-50 lbs of this in it as additional filtration. It cost me about 10 cents in US dollars to make this rock. Now thats a tough price to beat! Just another option to consider....
I have ordered rock from Dr. Foster and Smith's and DrMac&Sons. I was pleased with Dr Fosters until I recieved a 180lb shipment from DrMac. His pieces were shipped cheaper, reasonable priced and the pieces were very large which I needed for my 280gal.
If you are local, Coral Beauty beats the local competitors by a several dollars per lb. You can locate them via the sponsors link.