Other swimmers aren't so confident they should stick with what they've worn in the past.
Last week's ruling by FINA to approve more high-tech suits leaves them with some decisions to make.
Five-time Olympian Dara Torres expects to try different suits and make a last-minute decision. US team coach Mark Schubert said he would advise swimmers to experiment with various options and choose what they feel most comfortable with.
Phelps told The Associated Press he's sticking with Speedo.
"It's the only suit I've ever worn in my life," he said in a phone interview on Wednesday.
"I'm confident that I have the best suit on, and when I stand up on the block that's what I'm thinking."
The problem is that for many elite swimmers, their primary income comes from the suit manufacturer that sponsors them - and they may believe that company no longer makes the fastest suit.
"If you do wear what you think is the fastest suit and then you break a contract, it's a very, very delicate, tough situation," Torres said on a conference call on Wednesday, adding that other swimmers have talked to her about the dilemma.
The introduction of Speedo's NASA-designed LZR Racer suit 16 months ago sparked a flood of world records - and compelled some swimmers with contracts with other companies to compete in the LZR.
Now swimmers are wondering if newer suits by other manufacturers may be even faster.
The Jaked 01 and Arena X-Glide suits in particular are generating much buzz - and both are approved to be used at the US champs.
"Obviously athletes each have their own companies and have a desire to be successful," Schubert said on the conference call.
"That puts them in difficult situations. That's one reason we need to roll the suits back so that's less of a factor."
Speedo, which sponsors many of the top US swimmers, said on Tuesday it was "continuing to evaluate the situation internally." One of the few certainties for swimmers right now is that the high-tech suits will keep drawing plenty of attention at the nationals and then at the world championships this summer.
"It does take away from some things," Phelps said.
"A lot of swimmers are going to put up a lot of great times this summer, and a lot of it is going to be headlined by the suits. I just think it's not fair to other athletes and the athletes out there performing."
