For me, the best overall ride experience I have had has to be Big Thunder Mountain at Disneyland Paris. That is not to say, however, that is my favourite rollercoaster ever. Far from it, infact.
The best rollercoaster I have been on, for thrills, has to be Silver Star simply due to the phenomenal height and speeds which fail to relent over the impressive duration. However, that is not my favourite either.
For starts, nothing beats the superb drop into the crater on Nemesis Inferno, a ride which I reckon is really under-rated, even if it may play second fiddle in many eyes to Alton Towers classic.
Outside of a Disney ride, Europa Park's Poseidon, Alpenexpress and Euro-Mir rollercoasters are stunning, the latter also offering moments of great force as/if you plunge backwards through the 2nd half of the ride. Theming is also incredible, and, as someone put it - a satellite the size of Jodrell Bank stands next to Euro-Mir, merely as theming - and it even moves.
Other genuinely great rollercoasters I have been on include the relentless Tonnerre de Zeus, the speedy Trace du Hourrah and the enjoyable Air, but there is only one winner.
When there are no environmental conservation efforts, or DJ tents spoiling the atmosphere, Nemesis remains my best rollercoaster of all time, from those I have ridden. The proximity to the ground, individuality of this great masterpiece is simply what beats the other coasters hands down. The thing is, this ride wins overall. Sure, theming is better on other rides, force can be greater, so can speed - but this is a blend of all of these factors and as a result, it is simply the best! The likes of Oblivion and Rita are also good coasters, but the rush is over so, so fast, that Nemesis keeps it going for 40 od seconds!
Non-coaster-wise, my count is less than impressive. Europa Park's dark rides, whilst the theming is good, aren't amazing (Kassandra has little on Hex with exception to the moving seats), although the theming in the Tiroler Wildwasserbahn log flume is superb. Asterix offers the superb Oxygenarium, a bizarre water ride. Hex is a definite contender, and so is the great Samurai. But the winner? Pirates of the Carribean at Disneyland Paris! The magic, the depth, the queue. Amazing.