Well I have views for and against both formats. This is my (long) perspective:
Unlimited:
I started playing from NeoGen onwards yet started collecting since Baseset. I really used to enjoy Unlimited MUCH more than Modified, and now days, I still do. The fact that "almost" any deck (or combo with potential) could be played and have SOME form of success. This was mainly due to the vast range of drawing/searching trainers. Oak, Elm, Comp search, Item Finder, all made these decks possible. I tried a variety of deck ideas and combos and most of them went reasonably well, even though they werent too good in theory. With the amount of 'uber searching' you could do to get the cards you wanted just made anything playable which really added to the variety at our league. Unlimited was really fun because of this as there was a new deck each week and everyone had a different deck. This is one thing that Modified now lacks extremely. The fact that there is NO trainers that can draw cards which ARENT supporters is simply ridiculous. Why is it? Because we are stuck with TV Reporter, etc where we can draw like 3 cards per turn. Unlimited didnt have this, you could get what you wanted, when you wanted, from where you wanted, numerous times a turn. The 1 turn supporter rule cancels this out and the luck-factor of Modified went through the roof. Due to this 'lack of draw' the game is basically a Casino, where whoever gets the best draw wins, or whoever gets set up 1st. This is a MAJOR problem for Modified and numerous good players have left the game because of it. People say that Pidgeot and Magcargo should be banned because they're 'cheating'. Noone who played Unlimited would EVER say that. Those 2 cards are what balances the game and without them the game would be in an even worse position to where it is now...
However, with everything good there is something bad. Cards like SER, ER, Gust of Wind, Slowking, Sneasel, all made the game bad in its time. Of course everyone used those trainers in a deck since they were basic staple cards. How can you win if your opponent takes away your energy? You simply take away their energy. These led to an inbalance with the game however and 'practically' anything with 3+ energy cost was unplayable due to SER/ER. Gust also proved a problem. There was almost no hiding to where you were, bench or active. Cards like Chaos Gym and Slowking made Gust less effective but still caused a problem. With the release of new sets each time there are more and more possible combinations for Unlimited. However, it has now come to the point that there are only a few viable decks where others simply lose because of it. Decks like Blastoise/Suicune ex, Wiggly ex/Slowking/Sneasel, Aerojask, etc. They simply dominate because they are so effective. Oh and another ridiculous card was Erika's Jigglypuff... Umm, DCE=50 T1... broken. It ended alot of games T1/T2.
Modified:
Well, lets start by thinking about the good things about Modified. Atm, nothing immediately comes to mind as fast as Unlimited. A nice factor of the game is the rotation of sets. This can be good and this can be bad too. There have been times where we have lost our beloved cards which we desperately need due to the rotation. Good things about the rotation though. It doesnt allow for an infinate amount of combos since it restricts the amount of cards playable, eliminating everything that was good to bring in something new. It doesnt allow the full abuse of archetype combos over and over with extra boosts from new sets released. That is that main advantage of Modified.
There is though a LARGE amount of bad things about Modified. I'll continue on with the rotation. Bad things, like I said above, is the loss of good cards. When there is a card which is used so much because it allows so much benefits to any deck. These cards are usually the cards which holds the game together, but in the end, alot of people end up hating them because they're in every deck. Dunsparce (SS) was a major loss for the game. Not only could it bench fill but it could attack and stall in one. Nothing will ever replace it, yet the new Tauros and Luvdisc come close, but nothing near as good. Pidgeot and Magcargo are another thing. Everyone hates them because everyone uses them. Ask yourself, Why does everyone use them? I can imagine a stack of people saying stupid answers to that so i'll state the 'main' reason. The lack of draw due to the dependance on Supporters means there is a lack of draw and lack of getting what you want, when you need it. Unlimited NEVER had this problem, like I explained above. How else can we win if we dont have the right cards to win? Well we look for cards which can get us what we want. Pidgeot and Magcargo are a prime example of this, and after their rotation you will be seeing Porygon2 in every 2nd deck and that's a fact. People play cards to get what they want as quick as possible. The lack of draw also heavily increases the luck factor of the game. Like I said above, the game is now a Casino, where whoever has the most luck wins. The best starting hand compared to the worst will win if there is no way to get what you need. When you're stuck with a TV reporter which draws you 3 crappy cards and you cant play anything else, then you lose.
The thing that doesnt surprise me is that 85% of players around the world do NOT see this problem. Why dont they see it? Because they havent played Unlimited. You guys (as in 90% of members on this forum) are relatively new to the game, started playing the game from RS-on. You never experienced how easy it was to get what you wanted when you wanted, as many times as you want. This is what makes the game NOT fun. I see good players who Deserve to win because they are more skillful, but they dont because they lose due to hax luck. No deck in Modified is "Guaranteed" a win anymore, no matter how well it is built, due to Supporter dependance. We are practically FORCED to play Pidgeot and Magcargo to get which cards we need to win. It's sad and it makes alot of good players around the world angry.
I seriously hate playing Modified now, mainly due to the fact that it Isnt as fun as it USED to be. I feel like i'm playing for the sake of it, and not for fun anymore, mainly that I simply cannot let go of Pokemon and if I did then I would feel empty inside. Eventually this time will come and when it does I dont want it to be in a place where Modified looks like it does, I want the game to be skillful, fair and fun at the same time. Does anyone feel the same way as I do here?
Conclusion:
The game is getting worse and worse as newer sets are released. The game DESPERATELY needs drawing cards which are NOT supporters. This will make a stack of decks and combos much more playable and the reduce on heavy archetype playing throughout the entire world. Even if Bill and Prof Elm were re-printed then the game would be better, but noone sees that really and it's disappointing, however, I dont blame anyone since they havent experienced Unlimited and how the game 'should' be.
So my final verdict is that I simply prefer Unlimited over Modified for the reasons stated above. Unlimited has problems, but Modified has alot more problems, which, IMO, make it worse.
(Lol, did anyone actually read all of that? I've basically summed up the entire Unlimited and Modified formats in terms of practibility and fun.)