When you say "nitro" I assume you mean "glow" engines as the fuel is really alcohol and, if in the USA, may contain some nitro. On the other side of the pond, nitro is often not allowed as an additive. As to fuel, any of the major brands will do very well, most differences are just in the advertising. In most cases 5% to 10% nitro is quite enough (the less nitro the less expensive the fuel). Both synthetic or castor oil (or a mix of both) are quite suitable, no need to be particular. Unless you are running a very old Fox (which likes castor best) the synthetics work well with easier clean up from exhaust residue as long as you DO NOT RUN IT LEAN. A lean run on fuel with synthetic oil can overheat and ruin you engine quicker than a fuel with castor oil.