If you're a momentum investor and like to ride your winners, you probably love the biotech sector right now. After putting in a near-term bottom on June 27th, it's been almost a straight line up. That day was about a week before Biogen (BIIB) announced that its Alzheimer's drug has positive test results giving the sector yet another boost.If you're looking for biotech ETF options that are showing strong relative strength right now, there are three that are showing particular strength.iShares Nasdaq Biotechnology ETF (IBB)With nearly $10 billion in assets, IBB is the biggest biotech ETF. At the end of June, it was virtually unchanged on the year before the 10% run-up over the past few weeks. IBB is a market-cap weighted ETF that has roughly 30% of assets committed to the combination of Biogen, Amgen (AMGN), Celgene (CELG) and Gilead Sciences (GILD).Invesco Dynamic Biotech & Genome ETF (PBE)PBE is a roughly 30 stock portfolio that chooses companies based on a variety of investment merit criteria, including price momentum, earnings momentum, quality, management action, and value. Unlike IBB, it tends to spread its bets across companies of all sizes with 70% of assets going to small- and mid-cap stocks.VanEck Vectors Biotech ETF (BBH)BBH is perhaps the most concentrated biotech ETF. It simply holds the 25 largest biotech companies according to free float market cap weighting and has more than 60% of assets in the top 10 holdings. It's also the worst YTD performer with a total return of just 3%.My ETF Power Rankings available to ETF Focus subscribers have IBB at #2, BBH at #3 and PBE at #6 in the Biotech ETFs category, but I'd probably go with PBE out of these three. Especially in the biotech area, it's important to spread out risk. IBB and BBH are so top-heavy that it concentrates a lot of risk in just a few names. PBE dives further into smaller companies, but has its bets spread out a little further.What do you think? Are you adding to your biotech positions here? Comment down below!