Yes, Kym's POV has some merit, but, the main Q would still have to be: How good is the 2nd hand equipment? Will it cark it after a week?
Now, to the
lenses.
I see from the
Tamron site -
http://www.tamron.com.au/di-ii18-270_b008.html - that the 18-270 has some impressive specs.
It will give you that little extra zoom over the others (1.35 larger maximum image, in fact, or about a third bigger). Its "macro" capability is 1:3.8 - modest!
But it does have image stabilisation. (Sometimes I wonder if it's a good or bad thing for "learning" to take steady pics, but now I would not go w/o it.)
AND, it is compact. I do not know about its IQ, but usually T has a good name there.
On this page -
http://www.sigmaphoto.com/lenses/multi-purpose - note that
Sigma also makes an 18-250.
Yes, a tad less max. mag. than the
Tamron, but slightly better "macro" at 1:2.9.
Again, no idea of IQ, but usually not too bad.
Am.