If there is a best there must be a worst, so here are my five least favourite miniatures of all time. This is purely my own personnel taste and in no particular order. Off we go ...
Ork Warbike (2nd edition)
To me second edition orks are all amazing, however of all the models released the first plastic bikes just don't have that quirky charm. These feel like the beginning of the slow change from quirky fun orks to the current angry grim ork. The cult of speed I imagine is just not in keeping with this plastic model and I much prefer the old metal bikes that were released before. I own five of these plastic bikers (so far unpainted) and they just seem so uninspiring which is a shame.
He is iconic, he can fling the most spells, he is terrible in combat and this model really isn't very good. I'd always take the Advanced Heroquest or Warhammer Quest wizard over this guy if I could. I have tried painting him twice and both times I have not been convinced or enjoyed painting him. I don't know if it's the lack of detail or the staff being just a big stick but this well known wizard is a real struggle for me.
Giant (8th Edition)
I think my main problem with the current Giant that Games Workshop produce is that the paint job they give it looks like it isn't finished. That great big suspiciously 'plastic grey' shield/wheel is really distracting. Plus compared with the older giants be they Marauder or Albion he's just not as cool or imposing to my eye. His face also expresses a very dumb personality, not a fearsome centre piece for an army.
Biovore (2nd edition)
Tyranids need artillery apparently, how this guy got through as the answer to that is anyone's guess. Not a great model (the new one isn't much better!) and I'd be happy if they redesigned how Tyranids do long range shooting entirely, as this is just a cannon with legs and a face. On the other hand I think Spore mines are great fun, drifting 2d6 in random directions ready to go boom as they brush the lapel of an Imperial Guardsman!
When compiling this list I was trying to remember the name of that one model that I couldn't stand. A chaos space marine-daemon? that rides a bike and is about as reliable on the battlefield as an Ork Splatta Kannon. Doom Rider is that model. Looking like a cross between Ghost Rider & Venger off the Saturday morning cartoon Dungeons and Dragon and with a name that couldn't be more generic if you tried. I have no love for the Doom Rider mini either which is just a standard chaos space marine bike with a different head. With some decent fluff, some actual purpose behind him and a super crazy chaos bike he might become something interesting. As it is the idea of a chaos special character on a bike seemed more like filling a marketing hole than any actual cool mythology.