I think a lot of people disregard the fact that there can be stages that can be both competitive and unappealing and ones that are easily banned and fun.
For example, I found Melee's Battlefield and Yoshi's Story to be complete garbage in terms of design and much preferred Fountain of Dreams and Dreamland. The former two have aspects to them that are anti-competitive compared to other legal stages (in particular YS's absurdly small killbox and the ledge design of Battlefield which Brawl's Final Destination derived parts of it's horrid lip from) but are ultimately considered competitive because of their static nature, moderate size and lack of intrusive elements. There are plenty of competitively viable shapes for stages, and Project M caters to this well, but Melee sorely lacks a lot of these possible configurations.
On the flipside, stages like Norfair in Brawl are fun because they provide new strategies, though are not truly competitive because they have aspects which ruin comp gameplay (such as the ledges). If you're playing just for fun, odds are you aren't abusing the ledges to oblivion so you can enjoy ricocheting people off of the lavalfalls from the side or trying to force people to get hit by the lava tsunami. I'd like WarioWare a lot more if I could disable the bonuses when items are off though.
The problem is that most Smash stages go one extreme or another and rarely fall in a happy medium. For example, Melee, for most people, only has 6-competitively viable stages: one is flat, one is a transforming glitchy mess that people pardon for the sake of having a non-static stage (though two transfomations in particular would be instanty banned if they were static due to how they ruin the motion of a game) and the other four are derived from the same general design of three platforms situated triangularly above a solid platform. The other stages? Most of them are chaotic nightmares that are ultimately not fun to play on other than for asthetics, like Icicle Mountain and it's ridiculous scroll pacing or Flat Zone and it's tiny space. A lot of them would be potentially competitively viable if they didn't have aspects that ruined them (such as Green Greens and it's obnoxious blocks), but many of these problems also ruin it for people playing casually too. Brawl isn't much better off in this regard since I can't really see anyone thinking that Flat Zone 2 or 75m are fun if they were posed as brand new stages with no references to any actual Nintendo game. It does, however, have a lot more stages that can fall in the intermediate (like Delfino Plaza), but even then it's still a rather small amount of the whole roster. 64 was the closest of the three official titles to having a well balanced roster in terms of competitive and casual aspects.
Project M remedies this with several of it's stage designs. I'd like to see more stuff like Dracula's Castle, the retooled Port Town Aero Dive and Halberd, as they're designed to be fun both competitively and casually. Ideally, I'd like to see them retool something like Brinstar to be more competitive so that more comp stages exist with hazards, an unfortunate rarity.
Also, I do believe that Castle Siege should be static on the first platform; the walkoffs during the transformation are annoying at best and I find the first form to be the most interesting.
tl;dr: I prefer competitive versions of stages, but only if they have glaring aspects that make it feel necessary (such as the spire on Princess Peach's Castle, the giant second level of Castle Siege or the absurd damage that Port Town cars can deal, but not stuff like, say, if someone took away all of the weapons on Halberd or removing the bumpers from Princess Peach's Castle 64.)