This year, I shifted mine to Advantage Multi after doing a lot of research. I literally have a spreadsheet regarding the various products. I'm in South Louisiana -- major HW area, where dogs not on year-round prevention are virtually guaranteed to become infected.
I believe Multi is a very good product. The major downside is it's inconvenient, as compared to a flavored chew or flavored tab. It is it stinks when you apply it, and you have to remember not to pet your dog in that area on the back of the neck/shoulders. They have a greasy spot for a few days. You also have to be very careful that all of the product goes on the SKIN and not on the hair -- it's wasted if it's on the hair and your dog may not get enough of the active ingredient.
Here's why I switched to Advantage Multi from Iverhart Max (a Heartguard clone):
1. In the Auburn study, it's the ONLY product they tested that was 100% effective against the "resistant" strain of heartworm emerging in the Mississippi delta.
Heartworm preventive efficacy study results revealed at NAVC - DVM
DogAware.com News Archive: Heartworm Preventive Effectiveness
Where you are, resistance likely isn't a big deal (yet). Where I am, I keep hearing of people who had dogs on ivermectin (Heartgard, Tri-Heart Plus Iverhart, etc.) who claim they never missed a dose and their dogs tested HW +. Resistance has been rumored for years here, but it was typically explained away as owner compliance error (too late one month, missed a month, etc.). The Auburn study proved it's real.
I decided to switch from Iverhart Max to Advantage Multi because I want to be using the most effective product that exists: 2 of my 3 have already gone through HW treatment upon rescue. If I lived in California or the Northeast, where resistance hasn't been found yet, I'd likely still use a less expensive, ivermectin-based product.
2. Adv. Multi is one of only a few preventatives that protects against whipworms. Again, that's not a problem for most people as whips are rare. The shelter I pull many of my fosters from is infested with them though, so nearly everything comes out of there with whips (or hooks). Keeping my personal dogs on a product that protects against whips and hooks is thus important to me.
3. The flea protection is a bonus. It's been effective for me--we never see fleas. It gets rid of them on the foster dogs too.
4. The cost is better than Trifexis (I pay $14/mo. at KVsupply.com for Advantage Multi; Trifexis is $19/mo. With 3 dogs x 12 months, that $5 difference turns into $180/year saved).