Personally, I like MT4. I find it very intuitive. I've tried a couple of other platforms, but they didn't appeal to me. I'm sure there are better platforms, but I haven't had time to try them all.
There are some nasty stories around about some brokers using special broker-side plugins for MT4 where slippage can be "forced". I think it's quite possible, but don't have any proof.
EAs are a big subject of debate. Some people swear by them, others swear at them. Using a huge SL and small TP in an EA can really drive up the winning percentages, but usually fails in the long run. Other EAs work well, but only under certain market conditions. I've experimented with some exotic ones under development, but haven't personally tried out any of the commercial ones.