It depends on what your goals are, and how involved you want to get.  The 2 pools mentioned are ok if you want a 'set and forget' solution (middlecoin especially), however its not going to maximize your potential profits.  

Middlecoin is mining what is profitable and selling it in batches at market value at that time (my assumptions here, could be mistaken). Its basically letting someone else do the trading for you.  No holding, no potential to speculate or ride a coin to an increase in value (or a loss, of course).  In theory payments should be rather steady and consistent.

Multipool is giving you 'most profitable' at the time of mining, but of course that doesn't mean it translates in any way to when you actually have accumulated enough coins to sell them.  You end up with a bit of everything, and if you like to play the markets, and rode all the right swings, it could work out well for you.

Both these pools share the same characteristic; they are in it for short term small gains at the expense of potential significant long term gains.  Think of it this way, you could make an extra 5-10, maybe 15% profit mining many different coins and cashing them in, but what if you happened to mine nothing but 'the next ltc' (or even something that ends up half the price), while it was in its infancy and held them for long term growth.  The profit potential could be astronomical in comparison, but of course finding said coin isn't easy these days (hence this thread in the first place)

The other thing with these 2 pools is they are also more or less looking at coins already on an exchange (as far as I'm aware).  As was mentioned previously, its often newer coins not yet on an exchange that can lead to some very nice profits if you've picked the right one.

On a side note, my personal opinion is both of the above pools are doing harm to the current alt-coin crypto environment.  Middlecoin is trading bulk amounts of many different coins at market value on a daily basis, generally driving down prices, and multipool (and middlecoin) hammer coins when diff drops, leaving steady miners looking for long term gains slogging through higher difficulty times.  They both squeeze out room for speculation and real gains I mentioned elsewhere in this post, for the sake of much smaller short term profits.  They are both new enough that we may not see the longer term effects of this for awhile, but it may end up driving many coins to a 0 value game.  For this reason, I personally stay away.   However this personal opinion doesn't really change the rest of this reply, tried to give an unbiased view.

In the end, like most things, your probably going to get what you put into it.  If your able to put in the time, sift through a lot of noise, to find some diamonds in the rough, learn to understand and spot why one coin may end up worth more than others, the rewards are definitely there for the taking, and likely much greater than multi-pool solutions.  But if you don't have this time or aren't interested in getting your hands dirty with it, above 'set and forget' options are available!