YOU'VE SEEN the ads. They're all over the TV these days. A slick-looking stock broker out on the golf course bragging about how much money he's making at his client's expense. A tow-truck driver shrugging over the exotic houses he's bought with a pile of day-trading profits. Their message is hardly subtle -- You don't need some expensive sap telling you how to invest your money.

The revolution is clearly underway on Wall Street. It's the discount and online brokers vs. the high-fee status quo. Who needs a full-service guy when you can dial up Suretrade or Datek and make the transaction yourself for less than $10 a trade? Even mig hty Merrill Lynch, a veritable hive of full-service brokers, has gone online and lowered its fees for some services.

The truth is, the full-service brokers have left themselves open to attack. Too often, they fail to deliver the kind of value you're paying them for. Horror stories abound about the unscrupulous among them who induce you to buy and sell when you shouldn't merely to generate fees. Worse still are the ones who try to sell you inferior in-house investments with high commissions and mediocre returns.

But it's also true that a good broker (they do exist, of course) can offer invaluable counsel, especially if you lack the experience, time or interest to do your own research. With the discounters, you pretty much get what you pay for -- no advice, no res earch, no hand-holding. And in the case of online brokers it can get even worse: clogged servers, missing checks and hour-long waits on customer service lines.

Our view is that the new competition on Wall Street will make both sides better in the end, meaning investors will get improved service for lower costs. In the meantime, you have to decide for yourself how much help you really need and how much you're wil ling to pay for it. Here's what to consider...

Full-Service Brokers
Mahogany-paneled conference rooms, wing-tipped shoes, Wall Street addresses. The full-service category includes all the names that come to mind when we think of stockbrokers: Merrill Lynch, Salomon Smith Barney, Prudential. While these firms have higher c ommissions and fees than the discount brokers (much higher), they do offer a range of services and amenities the others do not.

Those begin with research and advice. During a bull market, when stocks are going up consistently, good ideas are a dime a dozen. But when the markets turn choppy, solid advice can save you. During periods of unpredictability, "the do-it-yourself investor s are left hanging in the wind with no one to turn to but themselves and the Internet chat columns," notes Michael Flanagan, an analyst with the Philadelphia research firm Financial Service Analytics. "Clients of full-service firms benefit from those firm s' strategies."

Some full-service firms offer a range of good mutual funds, estate-planning services and tax advice. A broker will set up a financial profile for you -- based on your assets, income and goals -- and advise you appropriately. All of this, of course, will c ost you.

If all you plan to do is buy some mutual funds and you know which ones you want, then paying a broker to round them up for you doesn't make much sense. Chances are, they don't sell through his firm, anyway. As for basic adv ice, we've got recommended picks in almost any category and can help you set up an asset-allocation plan, a retirement strategy or college tuition fund.

But if you want to buy individual stocks and lack the time or experience needed to do the research yourself, you might as well find a good broker. Ask around among your friends or colleagues -- you want someone you can trust.

If you do go the full-service route, there are several things to watch out for. First, make sure you get a commission schedule that spells out the fees you'll have to pay. It's also important to know how your broker is paid. Will he get higher commissions for selling certain financial products -- whether or not they're best for you? Always ask. At the very least, that will clue him in that you're on your toes.

Inquire, too, about accounts that let you pay an annual fee instead of per-trade commissions. For about 3% of your total assets, a broker will set you up with an asset-allocation program and make investment decisions accordingly. This eliminates the poten tial problem of "churning" -- when a broker unnecessarily trades your account to ratchet up extra commission fees.

Discount and Online Brokers
Our view is that many investors could make a lot more decisions on their own. That, of course, is what this site is all about. If you have a firm idea about a stock you want, why not get it as cheaply as you can?

Some discount brokers -- companies like Charles Schwab, Waterhouse Securities and Jack White -- are actually looking less and less like the pure order takers they used to be. They've been adding some advisory and account management services and they've be efed up their "mutual fund supermarket" offerings. The result is that they aren't as cheap as the pure online guys, but they aren't as expensive as the full-service brokers either.

Since most discounters have Web sites now, the lines have also blurred between discount and online-only brokers. True Internet upstarts like Suretrade, though, still offer rock-bottom trading costs and few frills. With a pure online broker you won't have the option of visiting a branch office to make a deposit in person or to speak with someone face to face. Your relationship will be limited to email and phone contacts.

While trading online can be cheap, it can also be a horror show. During times of high volume in the markets, servers can clog up and create extensive trading delays. You can call customer service to complain, but in some cases you'll wait as long as an ho ur. Checks get lost in the mail, orders go unfilled -- you name it.

Our view is that unless you trade a lot, you should avoid the deep discounters. They just aren't reliable enough yet.

Buying Mutual Funds
You have your choice here. You can either get your broker to pick you some funds -- accepting both high fees and limited choice. Or you can choose your own and buy them either straight from the fund company or through one of the new "mutual fund supermark ets."

If you favor the broker route, you'll likely be offered a set of "load" funds either run by the broker's firm or a mutual fund company they contract with. A load means you pay an upfront fee in addition to any ongoing expenses charged by the fund. Dependi ng on your time horizon -- that is, if you plan to own the fund for 10 years or more -- the fee might be worth it. But there are plenty of no-load funds out there that can get the job done for you.

To buy a no-load you can either call the fund company directly (our Fund Snapshots each have the 800 number), or you can go to one of the mutual fund "supermarkets" run by firms like Charles Schwab, Fidelity or Jack White. There, you'll pay a commission t o make the trade. But you'll have instant access to literally thousands of funds of all types.