What's the difference between...

Silver & gold boxes, coz as far as I can tell u can get the same things from them. But one costs 5 coins to open & other costs 10 coins

i believe in gold boxes you have a better chance of getting better rewards

I got a nugget from a gold box

As Nathan pointed out, you have a better chance of receiving a better reward.

and the cost to open a silver box is less than a gold box.

and the cost to open a silver box is less than a gold box.

Which most likely means better rewards from gold. As they said ^

I've heard there is a better chance of a good reward from a gold box and I've had about four or five, and I have always gotten enhancement stones, nugs and maybe a gem. But I've had a few silver boxes and I've gotten medals 50k money, a sceptor....it must be my luck. xD

i have opened 10 silver boxes and 10 gold boxes to test this,
gold boxes do have a better chance at obtaining better rewards. list as follows

Gold
------------
1. 41263 gold
2. crown
3. 21 coins
4. 11 enhancements stones
5. nugget
6.37452 gold
7.crown
8. gemstone
9. nugget
10. crown

silver
-----------
1. nugget
2. nugget
3. gemstone
4. 23184 gold
5. gemstone
6. 31746 gold
7. 8 coins
8. 11 coins
9. nugget
10. medal

Personally I like silver boxes more, ive opened a few gold boxes and nuggets seem to be the thing I get most. If thats the case id rather spend 5 coins for one and not ten each time.

i would go with the silver boxes too if i was to save coins. gold boxes are major gamblers and takes luck to win at it