You did not say what your budget looks like, but I vote for a combination jointer/planer machine. Having a wide jointer is really sweet, especially if it is the same width of your planer. These are not portable, light weight machines, but on par with industrial machinery in their materials, construction and heft. Grizzly, Jet, Rikon are the far east offerings. Hammer and Mini-Max the Euro options. Good luck and watch those fingers.
Combination jointer-planers machines are not so bad if you are buying a large and expensive stationary combination machine, but the inexpensive benchtop jointer-planer combinations essentially combine all the WORST features of both functions into one cheap and compact unit. Essentially you get what you pay for, but most people end up returning or selling off the benchtop combination units in rather short order. Benchtop planers can be quite good (I use a Dewalt DW735) but too many corners are cut in the benchtop combination units for them to even function as a quality planer and as jointers they often border on useless and have exceptionally short infeed and outfeed tables. The benchtop units also frequently suffer from inadequate damping mass and often lack sufficient structural stiffness for planing and jointing (there are just too many compromises).
While the large stationary combination machines can be quite good machines you really have to ask yourself whether the rare instances you might actually need to joint a 15-20" board (versus either a 6" or 8" jointer) warrants both the added cost up front plus the ongoing hassle of constantly swapping the machine between the two modes. You also have to ask if on those rare occasions you need more than 8" in jointer width whether the 15" or 20" afforded by a combination machine is sufficient to still joint the full desired width in a single operation or whether your table is likely to be more than 15-20" wide anyhow, thus necessitating other workarounds regardless, as well as whether you can reliably manhandle planks that are potentially several inches thick and many inches in width as they can be quite heavy (unless, of course, building with Balsa
). It is not uncommon to go jointer, planer, bandsaw, back to jointer or planer, back to bandsaw, back to jointer or planer, back and forth a few more times, back to jointer, back to planer for final thicknessing, etc. Having standalone machines, unless space is extremely tight, is often very desirable as you do not have to keep swapping modes and resetting all your depth settings with every change in operation when the machines are standalone.
For most of us an 8" jointer will suffice for probably close to 98-99% of everything we do and on the rare cases where we truly need to plane or joint an especially wide board, and can not rip it down the middle to split that difference for whatever reason, there are other options such as planer sleds and router jointing jigs, amongst other solutions. It often makes the most sense to focus on making certain whether the vast majority of your workflow will be facilitated by purchasing choices rather than possibly overbuying and trying to plan only around your most exceptional, and usually quite rare, capacity needs. I can honestly say that while I much prefer using a dedicated jointer for routine jointing and a dedicated planer for routine planing, I have had no problems using my planer to effectively joint those rare boards that truly needed to be kept more than 8" in width. I would not want to do all my jointing using planer, but for those rare and exceptional cases it is a perfectly acceptable solution.
My setup is a Jet JJ-8CS 8" jointer, a Dewalt DW735 benchtop planer (virtually no snipe), a Rikon 18" bandsaw for resawing boards plus a small 9" benchtop bandsaw (but I use this one mostly for cutting small items like circuit boards and sheet metal). Jointers and planers are effectively complimentary purchases and really go together in my opinion. Adding a bandsaw for resawing lumber to desired dimensions, when combined with an existing jointer and planer, then really expands your ability to process your own lumber and save by purchasing lumber in the rough and resawing to whatever dimensions your project requires.