Honestly, at 18 you are too young to be considering gear use. I am 28 and trained from 14-26 naturally. A lot of my friends did not even really grow until they were 21-24. I completely stopped gains and even lost weight for almost 2 years before I began using.
That being said, if you are going to use, keep the cycles light, there are far too many negative implications for a young guy. You can really screw up natural test production which does not slow until you are about my age. Try what was recommedned 10-12 weeks of sus/deca/d. Keep the doses moderate 250/200/20-25 mgs/dose.
You may even want to try only sust or deca with naps or anavar. Do not go overborad, more is not better in this game and you are too young to really know a lot. I still do not know everything and things are always changing and product evoloving.
Remeber recovery drugs clomid, clen. etc.