Lots of good advice above.
Gas. You will get long run times, but comes with problems. Gassers are loud, ridiculous loud. Draw's plenty of attention wanted or not. Heavy. To get full use of the gasser's you need a fairly good sized open area to run them. More so when you get up to the Baja or 5T size RC. Requires as much wrenching as anything else. Engine and ignition parts are expensive to replace when needed.
Nitro. Lots of wrenching. There's the time it takes to properly break in and tune. Messy. No matter how well tuned you are, there will always be left over exhaust residue to deal with. I love nitro and I love wrenching so for me nitro is fine. Run time can be what you want it to be. Most tanks only hold @5 ounces of fuel, so you have @ 10-15 minutes of run time to empty or practically limitless if you stop and top off the tank while still running. Always a good time to check temps at the same time anyway. Only real 'con' for me with nitro is the fuel costs. $30 a gallon for Byrons Gen2 25% is one small issue. Main issue is for me and the lack of an actual Local LHS, is that I am forced to make a half day run just to go purchase fuel.
Electric. With todays batteries and quality chargers there is a certain attraction for electric. No tuning. Just charge batteries, check radio settings and your RTR. But with electric, as mentioned, there is a far higher cost to have the convenience of that. Spend a little on 3000mah batteries and a wall wart charger and get fairly short run times along with slow charge times. Go lipo and you get longer run times, faster charging and huge power increase. But all that costs more as already mentioned above. With lipo, you can have some very serious cash invested in batteries and decent quality charger. Lipo's themselves do require extra attention and respect. You don't just put a lipo on the charger and 'set and forget'. You want to be right there making sure your not over heating the battery. Watching for the tell tale smoke that may precede a fire. Damage a lipo while running and they can smolder and cause a fire. Lipo do add to the fun factor as you go up in cell rating, as long as the ESC can handle the lipo can make acceleration and top speed crazy in comparison to nitro. But with those increases comes more wrenching from either the pure physical stress of the power there capable of, or from the increased potential of parts breakage that comes with high powered electrics.
So IMHO the best RC is what you want to run. All fuel types come with pro's and con's. All share some qualities. All have unique qualities. You really just need to weight out what would work out best for you. I have had a gas RC. I still have nitro and electrics. I love the sound of nitro. Electrics just don't inspire me to run them. I have a SCT and MT electric and am building a scaler. For the Scaler, electric is the only way to fly due to the fact that forcing a nitro to run slow is darn near impossible to do and still maintain slow course control. But speed of the SCT or MT without the buzz sound of the nitro just don't get me motivated to run them much. But that's my situation.
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