absolut

I need some help on deciding what tires to get. I finally got my two damaged rims replaced now I need some tires on 'em. The other two undamaged rims have Sumitomo HTR Z II 245/35/ZR20 w/ about 60% tread left. Now what I want to know is, should I replace all 4 tires or would I be ok with just replacing the two? I'd also like to know if I replace with the same tires or go with another brand or even different size? What would you reccomend for good tires w/ good treadlife?

Thanks.